Exhibit 10.4

ENERGY RECOVERY, INC.
2004 STOCK OPTION/STOCK ISSUANCE PLAN

ARTICLE ONE
GENERAL PROVISIONS

     I. PURPOSE OF THE PLAN

          This 2004 Stock Option/Stock Issuance Plan is intended to promote the interests of Energy Recovery Inc., a Delaware corporation, by providing eligible persons in the Corporation’s employ or service with the opportunity to acquire a proprietary interest, or otherwise increase their proprietary interest, in the Corporation as an incentive for them to continue in such employ or service.

          Capitalized terms herein shall have the meanings assigned to such terms in the attached Appendix.

     II. STRUCTURE OF THE PLAN

          A. The Plan shall be divided into two (2) separate equity programs:

               (i) the Option Grant Program under which eligible persons may, at the discretion of the Plan Administrator, be granted options to purchase shares of Common Stock, and

               (ii) the Stock Issuance Program under which eligible persons may, at the discretion of the Plan Administrator, be issued shares of Common Stock directly, either through the immediate purchase of such shares or as a bonus for services rendered the Corporation (or any Parent or Subsidiary).

          B. The provisions of Articles One and Four shall apply to both equity programs under the Plan and shall accordingly govern the interests of all persons under the Plan.

     III. ADMINISTRATION OF THE PLAN

          A. The Plan shall be administered by the Board. However, any or all administrative functions otherwise exercisable by the Board may be delegated to the Committee. Members of the Committee shall serve for such period of time as the Board may determine and shall be subject to removal by the Board at any time. The Board may also at any time terminate the functions of the Committee and reassume all powers and authority previously delegated to the Committee.

          B. The Plan Administrator shall have full power and authority (subject to the provisions of the Plan) to establish such rules and regulations as it may deem appropriate for proper administration of the Plan and to make such determinations under, and issue such interpretations of, the Plan and any outstanding options or stock issuances thereunder as it may deem necessary or advisable. Decisions of the Plan Administrator shall be final and binding on all parties who have an interest in the Plan or any option or stock issuance thereunder.

     IV. ELIGIBILITY

          A. The persons eligible to participate in the Plan are as follows:

               (i) Employees,

               (ii) non-employee members of the Board or the non-employee members of the board of directors of any Parent or Subsidiary, and

               (iii) consultants and other independent advisors who provide services to the Corporation (or any Parent or Subsidiary).

          B. The Plan Administrator shall have full authority to determine, (i) in respect of the grants under the Option Grant Program, which eligible persons are to receive the option grants, the time or times when those grants are to be made, the number of shares to be covered by each such grant, the status of the granted option as either an Incentive Option or a Non-Statutory Option, the time or times when each option is to become exercisable, the vesting schedule (if any) applicable to the option shares and the maximum term for which the option is to remain outstanding, and (ii) in respect of stock issuances under the Stock Issuance Program, which eligible persons are to receive stock issuances, the time or times when those issuances are to be made, the number of shares to be issued to each Participant, the vesting schedule (if any) applicable to the issued shares and the consideration to be paid by the Participant for such shares.

          C. The Plan Administrator shall have the absolute discretion either to grant options in accordance with the Option Grant Program or to effect stock issuances in accordance with the Stock Issuance Program.

     V. STOCK SUBJECT TO THE PLAN

          A. The stock issuable under the Plan shall be shares of authorized but unissued or reacquired Common Stock. The maximum number of shares of Common Stock which may be issued over the term of the Plan shall not exceed eight hundred fifty thousand (850,000) shares.

          B. Shares of Common Stock subject to outstanding options shall be available for subsequent issuance under the Plan to the extent (i) the options expire or terminate for any reason prior to exercise in full or (ii) the options are cancelled in accordance with the cancellation-regrant provisions of Article Two. Unvested shares issued under the Plan and subsequently repurchased by the Corporation, at the option exercise or direct issue price paid per share, pursuant to the Corporation’s repurchase rights under the Plan shall be added back to the number of shares of Common Stock reserved for issuance under the Plan and shall accordingly be available for reissuance through one or more subsequent option grants or direct stock issuances under the Plan.

          C. Should any change be made to the Common Stock by reason of any stock split, stock dividend, recapitalization, combination of shares, exchange of shares or other change affecting the outstanding Common Stock as a class without the Corporation’s receipt of consideration, appropriate adjustments shall be made to (i) the maximum number and/or class of

securities issuable under the Plan and (ii) the number and/or class of securities and the exercise price per share in effect under each outstanding option in order to prevent the dilution or enlargement of benefits thereunder. The adjustments determined by the Plan Administrator shall be final, binding and conclusive. In no event shall any such adjustments be made in connection with the conversion of one or more outstanding shares of the Corporation’s preferred stock into shares of Common Stock.

ARTICLE TWO
OPTION GRANT PROGRAM

     I. OPTION TERMS

          Each option shall be evidenced by one or more documents in the form approved by the Plan Administrator; provided, however, that each such document shall comply with the terms specified below. Each document evidencing an Incentive Option shall, in addition, be subject to the provisions of the Plan applicable to such options.

          A. Exercise Price.

               1. The exercise price per share shall be fixed by the Plan Administrator in accordance with the following provisions:

               (i) The exercise price per share shall not be less than eighty-five percent (85%) of the Fair Market Value per share of Common Stock on the option grant date.

               (ii) If the person to whom the option is granted is a 10% Stockholder, then the exercise price per share shall not be less than one hundred ten percent (110%) of the Fair Market Value per share of Common Stock on the option grant date.

               2. The exercise price shall become immediately due upon exercise of the option and shall, subject to the provisions of Section I of Article Four and the documents evidencing the option, be payable in cash or check made payable to the Corporation. Should the Common Stock be registered under Section 12 of the 1934 Act at the time the option is exercised, then the exercise price may also be paid as follows:

               (i) in shares of Common Stock held for the requisite period necessary to avoid a charge to the Corporation’s earnings for financial reporting purposes and valued at Fair Market Value on the Exercise Date, or

               (ii) to the extent the option is exercised for vested shares, through a special sale and remittance procedure pursuant to which the Optionee shall concurrently provide irrevocable instructions (A) to a Corporation-designated brokerage firm to effect the immediate sale of the purchased shares and remit to the Corporation, out of the sale proceeds available on the settlement date, sufficient funds to cover the aggregate exercise price payable for the purchased shares plus all applicable Federal, state and local income and employment taxes required to be withheld by the Corporation by reason of such exercise and (B) to the Corporation to deliver the certificates for the purchased shares directly to such brokerage firm in order to complete the sale.

          Except to the extent such sale and remittance procedure is utilized, payment of the exercise price for the purchased shares must be made on the Exercise Date.

          B. Exercise and Term of Options. Each option shall be exercisable at such time or times, during such period and for such number of shares as shall be determined by the Plan Administrator and set forth in the documents evidencing the option grant. However, no option shall have a term in excess of ten (10) years measured from the option grant date.

          C. Effect of Termination of Service.

               1. The following provisions shall govern the exercise of any options held by the Optionee at the time of cessation of Service or death:

               (i) Should the Optionee cease to remain in Service for any reason other than death, Disability or Misconduct, then the Optionee shall have a period of one (1) month following the date of such cessation of Service during which to exercise each outstanding option held by such Optionee.

               (ii) Should Optionee’s Service terminate by reason of Disability, then the Optionee shall have a period of twelve (12) months following the date of such cessation of Service during which to exercise each outstanding option held by such Optionee.

               (iii) If the Optionee dies while holding an outstanding option, then the personal representative of his or her estate or the person or persons to whom the option is transferred pursuant to the Optionee’s will or the laws of inheritance shall have a twelve (12)-month period following the date of the Optionee’s death to exercise such option.

               (iv) Under no circumstances, however, shall any such option be exercisable after the specified expiration of the option term.

               (v) During, the applicable post-Service exercise period, the option may not be exercised in the aggregate for more than the number of vested shares for which the option is exercisable on the date of the Optionee’s cessation of Service. Upon the expiration of the applicable exercise period or (if earlier) upon the expiration of the option term, the option shall terminate and cease to be outstanding for any vested shares for which the option has not been exercised. However, the option shall, immediately upon the Optionee’s cessation of Service, terminate and cease to be outstanding in respect of any and all option shares for which the option is not otherwise at the time exercisable or in which the Optionee is not otherwise at that time vested.

               (vi) Should Optionee’s Service be terminated for Misconduct, then all outstanding options held by the Optionee shall terminate immediately and cease to remain outstanding.

               2. The Plan Administrator shall have the discretion, exercisable either at the time an option is granted or at any time while the option remains outstanding, to:

               (i) extend the period of time for which the option is to remain exercisable following Optionee’s cessation of Service or death from the limited period otherwise in effect for that option to such greater period of time as the Plan Administrator shall deem appropriate, but in no event beyond the expiration of the option term, and/or

               (ii) permit the option to be exercised, during the applicable post-Service exercise period, not only in respect of the number of vested shares of Common Stock for which such option is exercisable at the time of the Optionee’s cessation of Service but also in respect of one or more additional installments in which the Optionee would have vested under the option had the Optionee continued in Service.

          D. Stockholder Rights. The holder of an option shall have no stockholder rights in respect of the shares subject to the option until such person shall have exercised the option, paid the exercise price and become the recordholder of the purchased shares.

          E. Unvested Shares. The Plan Administrator shall have the discretion to grant options which are exercisable for unvested shares of Common Stock. Should the Optionee cease Service while holding such unvested shares, the Corporation shall have the right to repurchase, at the exercise price paid per share, any or all of those unvested shares. The terms upon which such repurchase right shall be exercisable (including the period and procedure for exercise and the appropriate vesting schedule for the purchased shares) shall be established by the Plan Administrator and set forth in the document evidencing such repurchase right. The Plan Administrator may not impose a vesting schedule upon the option grant or any shares of Common Stock subject to that option which is more restrictive than twenty percent (20%) per year vesting, with the initial vesting to occur not later than one (1) year after the option grant date. However, such limitation shall not be applicable to any option grants made to individuals who are officers of the Corporation, non-employee Board members or independent consultants.

          F. First Refusal Rights. Until such time as the Common Stock is first registered under Section 12 of the 1934 Act, the Corporation shall have the right of first refusal in respect of any proposed disposition by the Optionee (or any successor in interest) of any shares of Common Stock issued under the Plan. Such right of first refusal shall be exercisable in accordance with the terms established by the Plan Administrator and set forth in the document evidencing such right.

          G. Limited Transferability of Options. During the lifetime of the Optionee, the option shall be exercisable only by the Optionee and shall not be assignable or transferable other than by will or by the laws of descent and distribution following the Optionee’s death.

          H. Withholding. The Corporation’s obligation to deliver shares of Common Stock upon the exercise of any options granted under the Plan shall be subject to the satisfaction of all applicable Federal, state and local income and employment tax withholding requirements.

     II. INCENTIVE OPTIONS

          The terms specified below shall be applicable to all Incentive Options. Except as modified by the provisions of this Section II, all the provisions of the Plan shall be applicable to Incentive Options. Options which are specifically designated as Non-Statutory Options shall not be subject to the terms of this Section II.

          A. Eligibility. Incentive Options may only be granted to Employees.

          B. Exercise Price. The exercise price per share shall not be less than one hundred percent (100%) of the Fair Market Value per share of Common Stock on the option grant date.

          C. Dollar Limitation. The aggregate Fair Market Value of the shares of Common Stock (determined as of the respective date or dates of grant) for which one or more options granted to any Employee under the Plan (or any other option plan of the Corporation or any Parent or Subsidiary) may for the first time become exercisable as Incentive Options during any one (1) calendar year shall not exceed the sum of One Hundred Thousand Dollars ($100,000). To the extent the Employee holds two (2) or more such options which become exercisable for the first time in the same calendar year, the foregoing limitation on the exercisability of such options as Incentive Options shall be applied on the basis of the order in which such options are granted.

          D. 10% Stockholder. If any Employee to whom an Incentive Option is granted is a 10% Stockholder, then the option term shall not exceed five (5) years measured from the option grant date.

     III. CORPORATE TRANSACTION

          A. The shares subject to each option outstanding under the Plan at the time of a Corporate Transaction shall automatically vest in full so that each such option shall, immediately prior to the effective date of the Corporate Transaction, become fully exercisable for all of the shares of Common Stock at the time subject to that option and may be exercised for any or all of those shares as fully-vested shares of Common Stock. However, the shares subject to an outstanding option shall not vest on such an accelerated basis if and to the extent: (i) such option is assumed by the successor corporation (or parent thereof) in the Corporate Transaction and the Corporation’s repurchase rights in respect of the unvested option shares are concurrently assigned to such successor corporation (or parent thereof) or (ii) such option is to be replaced with a cash incentive program of the successor corporation which preserves the spread existing on the unvested option shares at the time of the Corporate Transaction and provides for subsequent payout in accordance with the same vesting schedule applicable to those unvested option shares or (iii) the acceleration of such option is subject to other limitations imposed by the Plan Administrator at the time of the option grant.

          B. All outstanding repurchase rights shall also terminate automatically, and the shares of Common Stock subject to those terminated rights shall immediately vest in full, in the event of any Corporate Transaction, except to the extent: (i) those repurchase rights are assigned to the successor corporation (or parent thereof) in connection with such Corporate

     IV. CANCELLATION AND REGRANT OF OPTIONS

          The Plan Administrator shall have the authority to effect, at any time and from time to time, with the consent of the affected option holders, the cancellation of any or all outstanding options under the Plan and to grant in substitution therefor new options covering the same or different number of shares of Common Stock but with an exercise price per share based on the Fair Market Value per share of Common Stock on the new option grant date.

ARTICLE THREE
STOCK ISSUANCE PROGRAM

     I. STOCK ISSUANCE TERMS

          Shares of Common Stock may be issued under the Stock Issuance Program through direct and immediate issuances without any intervening option grants. Each such stock issuance shall be evidenced by a Stock Issuance Agreement which complies with the terms specified below.

          A. Purchase Price.

               1. The purchase price per share shall be fixed by the Plan Administrator but shall not be less than eighty-five percent (85%) of the Fair Market Value per share of Common Stock on the issue date. However, the purchase price per share of Common Stock issued to a 10% Stockholder shall not be less than one hundred and ten percent (110%) of such Fair Market Value.

               2. Subject to the provisions of Section I of Article Four, shares of Common Stock may be issued under the Stock Issuance Program for any of the following items of consideration which the Plan Administrator may deem appropriate in each individual instance:

               (i) cash or check made payable to the Corporation, or

               (ii) past services rendered to the Corporation (or any Parent or Subsidiary).

          B. Vesting Provisions.

               1. Shares of Common Stock issued under the Stock Issuance Program may, in the discretion of the Plan Administrator, be fully and immediately vested upon issuance or may vest in one or more installments over the Participant’s period of Service or upon attainment of specified performance objectives. However, the Plan Administrator may not impose a vesting schedule upon any stock issuance effected under the Stock Issuance Program which is more restrictive than twenty percent (20%) per year vesting, with initial vesting to occur not later than one (1) year after the issuance date. Such limitation shall not apply to any Common Stock issuances made to the officers of the Corporation, non-employee Board members or independent consultants.

               2. Any new, substituted or additional securities or other property (including money paid other than as a regular cash dividend) which the Participant may have the right to receive in respect of the Participant’s unvested shares of Common Stock by reason of any stock dividend, stock split, recapitalization, combination of shares, exchange of shares or other change affecting the outstanding Common Stock as a class without the Corporation’s receipt of consideration shall be issued subject to (i) the same vesting requirements applicable to the Participant’s unvested shares of Common Stock and (ii) such escrow arrangements as the Plan Administrator shall deem appropriate.

               3. The Participant shall have full stockholder rights in respect of any shares of Common Stock issued to the Participant under the Stock Issuance Program, whether or not the Participant’s interest in those shares is vested. Accordingly, the Participant shall have the right to vote such shares and to receive any regular cash dividends paid on such shares.

               4. Should the Participant cease to remain in Service while holding one or more unvested shares of Common Stock issued under the Stock Issuance Program or should the performance objectives not be attained in respect of one or more such unvested shares of Common Stock, then those shares shall be immediately surrendered to the Corporation for cancellation, and the Participant shall have no further stockholder rights in respect of those shares. To the extent the surrendered shares were previously issued to the Participant for consideration paid in cash or cash equivalent (including the Participant’s purchase-money indebtedness), the Corporation shall repay to the Participant the cash consideration paid for the surrendered shares and shall cancel the unpaid principal balance of any outstanding purchase- money note of the Participant attributable to such surrendered shares.

               5. The Plan Administrator may in its discretion waive the surrender and cancellation of one or more unvested shares of Common Stock (or other assets attributable thereto) which would otherwise occur upon the non-completion of the vesting schedule applicable to such shares. Such waiver shall result in the immediate vesting of the Participant’s interest in the shares of Common Stock as to which the waiver applies. Such waiver may be effected at any time, whether before or after the Participant’s cessation of Service or the attainment or non-attainment of the applicable performance objectives.

          C. First Refusal Rights. Until such time as the Common Stock is first registered under Section 12 of the 1934 Act, the Corporation shall have the right of first refusal in respect of any proposed disposition by the Participant (or any successor in interest) of any shares of Common Stock issued under the Stock Issuance Program. Such right of first refusal shall be exercisable in accordance with the terms established by the Plan Administrator and set forth in the document evidencing such right.

     II. CORPORATE TRANSACTION

          A. Upon the occurrence of a Corporate Transaction, all outstanding repurchase rights under the Stock Issuance Program shall terminate automatically, and the shares of Common Stock subject to those terminated rights shall immediately vest in full, except to the extent: (i) those repurchase rights are assigned to the successor corporation (or parent thereof) in connection with such Corporate Transaction or (ii) such accelerated vesting is precluded by other limitations imposed by the Plan Administrator at the time the repurchase right is issued.

          B. The Plan Administrator shall have the discretionary authority, exercisable either at the time the unvested shares are issued or any time while the Corporation’s repurchase rights in respect of those shares remain outstanding, to provide that those rights shall automatically terminate on an accelerated basis, and the shares of Common Stock subject to those terminated rights shall immediately vest, in the event the Participant’s Service should subsequently terminate by reason of an Involuntary Termination within a designated period (not

ARTICLE FOUR

MISCELLANEOUS

     I. FINANCING

          The Plan Administrator may permit any Optionee or Participant to pay the option exercise price or the purchase price for shares issued to such person under the Plan by delivering a full-recourse, interest-bearing promissory note payable in one or more installments and secured by the purchased shares. However, any promissory note delivered by a consultant must be secured by collateral in addition to the purchased shares of Common Stock. In no event shall the maximum credit available to the Optionee or Participant exceed the sum of (i) the aggregate option exercise price or purchase price payable for the purchased shares plus (ii) any Federal, state and local income and employment tax liability incurred by the Optionee or the Participant in connection with the option exercise or share purchase.

     II. EFFECTIVE DATE AND TERM OF PLAN

          A. The Plan shall become effective when adopted by the Board, but no option granted under the Plan may be exercised, and no shares shall be issued under the Plan, until the Plan is approved by the Corporation’s stockholders. If such stockholder approval is not obtained within twelve (12) months after the date of the Board’s adoption of the Plan, then all options previously granted under the Plan shall terminate and cease to be outstanding, and no further options shall be granted and no shares shall be issued under the Plan. Subject to such limitation, the Plan Administrator may grant options and issue shares under the Plan at any time after the effective date of the Plan and before the date fixed herein for termination of the Plan.

          B. The Plan shall terminate upon the earliest of (i) the expiration of the ten (10)-year period measured from the date the Plan is adopted by the Board, (ii) the date on which all shares available for issuance under the Plan shall have been issued as vested shares or (iii) the termination of all outstanding options in connection with a Corporate Transaction. All options and unvested stock issuances outstanding at that time under the Plan shall continue to have full force and effect in accordance with the provisions of the documents evidencing such options or issuances.

     III. AMENDMENT OF THE PLAN

          A. The Board shall have complete and exclusive power and authority to amend or modify the Plan in any or all respects. However, no such amendment or modification shall adversely affect the rights and obligations in respect of options or unvested stock issuances at the time outstanding under the Plan unless the Optionee or the Participant consents to such amendment or modification. In addition, certain amendments may require stockholder approval pursuant to applicable laws and regulations.

          B. Options may be granted under the Option Grant Program and shares may be issued under the Stock Issuance Program which are in each instance in excess of the number of shares of Common Stock then available for issuance under the Plan, provided any excess shares actually issued under those programs shall be held in escrow until there is obtained stockholder approval of an amendment sufficiently increasing the number of shares of Common

Stock available for issuance under the Plan. If such stockholder approval is not obtained within twelve (12) months after the date the first such excess issuances are made, then (i) any unexercised options granted on the basis of such excess shares shall terminate and cease to be outstanding and (ii) the Corporation shall promptly refund to the Optionees and the Participants the exercise or purchase price paid for any excess shares issued under the Plan and held in escrow, together with interest (at the applicable Short Term Federal Rate) for the period the shares were held in escrow, and such shares shall thereupon be automatically cancelled and cease to be outstanding.

     IV. USE OF PROCEEDS

          Any cash proceeds received by the Corporation from the sale of shares of Common Stock under the Plan shall be used for general corporate purposes.

     V. WITHHOLDING

          The Corporation’s obligation to deliver shares of Common Stock upon the exercise of any options or upon the issuance or vesting of any shares issued under the Plan shall be subject to the satisfaction of all applicable Federal, state and local income and employment tax withholding requirements.

     VI. REGULATORY APPROVALS

          The implementation of the Plan, the granting of any options under the Plan and the issuance of any shares of Common Stock (i) upon the exercise of any option or (ii) under the Stock Issuance Program shall be subject to the Corporation’s procurement of all approvals and permits required by regulatory authorities having jurisdiction over the Plan, the options granted under it and the shares of Common Stock issued pursuant to it.

     VII. NO EMPLOYMENT OR SERVICE RIGHTS

          Nothing in the Plan shall confer upon the Optionee or the Participant any right to continue in Service for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Corporation (or any Parent or Subsidiary employing or retaining such person) or of the Optionee or the Participant, which rights are hereby expressly reserved by each, to terminate such person’s Service at any time for any reason, with or without cause.

     VIII. FINANCIAL REPORTS

          The Corporation shall deliver a balance sheet and an income statement at least annually to each individual holding an outstanding option under the Plan, unless such individual is a key Employee whose duties in connection with the Corporation (or any Parent or Subsidiary) assure such individual access to equivalent information.

APPENDIX

          The following definitions shall be in effect under the Plan:

          A. Board shall mean the Corporation’s Board of Directors.

          B. Code shall mean the Internal Revenue Code of 1986, as amended.

          C. Committee shall mean a committee of two (2) or more Board members appointed by the Board to exercise one or more administrative functions under the Plan.

          D. Common Stock shall mean the Corporation’s common stock.

          E. Corporate Transaction shall mean either of the following stockholder-approved transactions to which the Corporation is a party:

               (i) a merger or consolidation in which securities possessing more than fifty percent (50%) of the total combined voting power of the Corporation’s outstanding securities are transferred to a person or persons different from the persons holding those securities immediately prior to such transaction, or

               (ii) the sale, transfer or other disposition of all or substantially all of the Corporation’s assets in complete liquidation or dissolution of the Corporation.

          F. Corporation shall mean Energy Recovery Inc., a Delaware corporation, and any successor corporation to all or substantially all of the assets or voting stock of Energy Recovery Inc. which shall by appropriate action adopt the Plan.

          G. Disability shall mean the inability of the Optionee or the Participant to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment and shall be determined by the Plan Administrator on the basis of such medical evidence as the Plan Administrator deems warranted under the circumstances.

          H. Employee shall mean an individual who is in the employ of the Corporation (or any Parent or Subsidiary), subject to the control and direction of the employer entity as to both the work to be performed and the manner and method of performance.

          I. Exercise Date shall mean the date on which the Corporation shall have received written notice of the option exercise.

          J. Fair Market Value per share of Common Stock on any relevant date shall be determined in accordance with the following provisions:

               (i) If the Common Stock is at the time traded on the Nasdaq National Market, then the Fair Market Value shall be the closing selling price per share of Common Stock on the date in question, as such price is reported

by the National Association of Securities Dealers on the Nasdaq National Market or any successor system. If there is no closing selling price for the Common Stock on the date in question, then the Fair Market Value shall be the closing selling price on the last preceding date for which such quotation exists.

               (ii) If the Common Stock is at the time listed on any Stock Exchange, then the Fair Market Value shall be the closing selling price per share of Common Stock on the date in question on the Stock Exchange determined by the Plan Administrator to be the primary market for the Common Stock, as such price is officially quoted in the composite tape of transactions on such exchange. If there is no closing selling price for the Common Stock on the date in question, then the Fair Market Value shall be the closing selling price on the last preceding date for which such quotation exists.

               (iii) If the Common Stock is at the time neither listed on any Stock Exchange nor traded on the Nasdaq National Market, then the Fair Market Value shall be determined by the Plan Administrator after taking into account such factors as the Plan Administrator shall deem appropriate.

          K. Incentive Option shall mean an option which satisfies the requirements of Code Section 422.

          L. Involuntary Termination shall mean the termination of the Service of any individual which occurs by reason of:

               (i) such individual’s involuntary dismissal or discharge by the Corporation for reasons other than Misconduct, or

               (ii) such individual’s voluntary resignation following (A) a change in his or her position with the Corporation which materially reduces his or her duties and responsibilities or the level of management to which he or she reports, (B) a reduction in his or her level of compensation (including base salary, fringe benefits and target bonuses under any corporate-performance based bonus or incentive programs) by more than fifteen percent (15%) or (C) a relocation of such individual’s place of employment by more than fifty (50) miles, provided and only if such change, reduction or relocation is effected without the individual’s consent.

          M. Misconduct shall mean the commission of any act of fraud, embezzlement or dishonesty by the Optionee or Participant, any unauthorized use or disclosure by such person of confidential information or trade secrets of the Corporation (or any Parent or Subsidiary), or any other intentional misconduct by such person adversely affecting the business or affairs of the Corporation (or any Parent or Subsidiary) in a material manner. The foregoing definition shall not be deemed to be inclusive of all the acts or omissions which the Corporation (or any Parent or Subsidiary) may consider as grounds for the dismissal or discharge of any Optionee, Participant or other person in the Service of the Corporation (or any Parent or Subsidiary).

          N. 1934 Act shall mean the Securities Exchange Act of 1934, as amended.

          O. Non-Statutory Option shall mean an option not intended to satisfy the requirements of Code Section 422.

          P. Option Grant Program shall mean the option grant program in effect under the Plan.

          Q. Optionee shall mean any person to whom an option is granted under the Plan.

          R. Parent shall mean any corporation (other than the Corporation) in an unbroken chain of corporations ending with the Corporation, provided each corporation in the unbroken chain (other than the Corporation) owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

          S. Participant shall mean any person who is issued shares of Common Stock under the Stock Issuance Program.

          T. Plan shall mean the Corporation’s 2004 Stock Option/Stock Issuance Plan, as set forth in this document.

          U. Plan Administrator shall mean either the Board or the Committee acting in its capacity as administrator of the Plan.

          V. Service shall mean the provision of services to the Corporation (or any Parent or Subsidiary) by a person in the capacity of an Employee, a non-employee member of the board of directors or a consultant or independent advisor, except to the extent otherwise specifically provided in the documents evidencing the option grant.

          W. Stock Exchange shall mean either the American Stock Exchange or the New York Stock Exchange.

          X. Stock Issuance Agreement shall mean the agreement entered into by the Corporation and the Participant at the time of issuance of shares of Common Stock under the Stock Issuance Program.

          Y. Stock Issuance Program shall mean the stock issuance program in effect under the Plan.

          Z. Subsidiary shall mean any corporation (other than the Corporation) in an unbroken chain of corporations beginning with the Corporation, provided each corporation (other than the last corporation) in the unbroken chain owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

          AA. 10% Stockholder shall mean the owner of stock (as determined under Code Section 424(d)) possessing more than ten percent (10%) of the total combined voting power of all classes of stock of the Corporation (or any Parent or Subsidiary).

Plan History

Adopted by the Board of Directors at a Regular Meeting held on ___ _________2004.

Ratified by the Stockholders at the 2004 Annual Meeting held on ___ _________ 2004.

ENERGY RECOVERY, INC.
STOCK PURCHASE AGREEMENT

          AGREEMENT made this ___day of _________ 2004, by and between Energy Recovery, Inc., a Delaware corporation, and ______, Optionee under the Corporation’s 2004 Stock Option/Stock Issuance Plan.

          All capitalized terms in this Agreement shall have the meaning assigned to them in this Agreement or in the attached Appendix.

     A. EXERCISE OF OPTION

          1. Exercise. Optionee hereby purchases ____________ shares of Common Stock (the “Purchased Shares”) pursuant to that certain option (the “Option”) granted Optionee on _______ (the “Grant Date”) to purchase up to ______ shares of Common Stock (the “Option Shares”) under the Plan at the exercise price of $______ per share (the “Exercise Price”).

          2. Payment. Concurrently with the delivery of this Agreement to the Corporation, Optionee shall pay the Exercise Price for the Purchased Shares in accordance with the provisions of the Option Agreement and shall deliver whatever additional documents may be required by the Option Agreement as a condition for exercise, together with a duly-executed blank Assignment Separate from Certificate (in the form attached hereto as Exhibit I) with respect to the Purchased Shares.

          3. Stockholder Rights. Until such time as the Corporation exercises the Repurchase Right or the First Refusal Right, Optionee (or any successor in interest) shall have all the rights of a stockholder (including voting, dividend and liquidation rights) with respect to the Purchased Shares, subject, however, to the transfer restrictions of Articles B and C.

     B. SECURITIES LAW COMPLIANCE

          1. Restricted Securities. The Purchased Shares have not been registered under the 1933 Act and are being issued to Optionee in reliance upon the exemption from such registration provided by SEC Rule 701 for stock issuances under compensatory benefit plans such as the Plan. Optionee hereby confirms that Optionee has been informed that the Purchased Shares are restricted securities under the 1933 Act and may not be resold or transferred unless the Purchased Shares are first registered under the Federal securities laws or unless an exemption from such registration is available. Accordingly, Optionee hereby acknowledges that Optionee is prepared to hold the Purchased Shares for an indefinite period and that Optionee is aware that SEC Rule 144 issued under the 1933 Act which exempts certain resales of unrestricted securities is not presently available to exempt the resale of the Purchased Shares from the registration requirements of the 1933 Act.

          2. Restrictions on Disposition of Purchased Shares. Optionee shall make no disposition of the Purchased Shares (other than a Permitted Transfer) unless and until there is compliance with all of the following requirements:

               (i) Optionee shall have provided the Corporation with a written summary of the terms and conditions of the proposed disposition.

               (ii) Optionee shall have complied with all requirements of this Agreement applicable to the disposition of the Purchased Shares.

               (iii) Optionee shall have provided the Corporation with written assurances, in form and substance satisfactory to the Corporation, that (a) the proposed disposition does not require registration of the Purchased Shares under the 1933 Act or (b) all appropriate action necessary for compliance with the registration requirements of the 1933 Act or any exemption from registration available under the 1933 Act (including Rule 144) has been taken.

          The Corporation shall not be required (i) to transfer on its books any Purchased Shares which have been sold or transferred in violation of the provisions of this Agreement or (ii) to treat as the owner of the Purchased Shares, or otherwise to accord voting, dividend or liquidation rights to, any transferee to whom the Purchased Shares have been transferred in contravention of this Agreement.

          3. Restrictive Legends. The stock certificates for the Purchased Shares shall be endorsed with one or more of the following restrictive legends:

     “The shares represented by this certificate have not been registered under the Securities Act of 1933. The shares may not be sold or offered for sale in the absence of (a) an effective registration statement for the shares under such Act, (b) a “no action” letter of the Securities and Exchange Commission with respect to such sale or offer or (c) satisfactory assurances to the Corporation that registration under such Act is not required with respect to such sale or offer.”

     “The shares represented by this certificate are subject to certain repurchase rights and rights of first refusal granted to the Corporation and accordingly may not be sold, assigned, transferred, encumbered, or in any manner disposed of except in conformity with the terms of a written agreement dated ______, 2004 between the Corporation and the registered holder of the shares (or the predecessor in interest to the shares). A copy of such agreement is maintained at the Corporation’s principal corporate offices.”

     C. TRANSFER RESTRICTIONS

          1. Restriction on Transfer. Except for any Permitted Transfer, Optionee shall not transfer, assign, encumber or otherwise dispose of any of the Purchased Shares which are subject to the Repurchase Right. In addition, Purchased Shares which are released from the Repurchase Right shall not be transferred, assigned, encumbered or otherwise disposed of in contravention of the First Refusal Right or the Market Stand-Off.

          2. Transferee Obligations. Each person (other than the Corporation) to whom the Purchased Shares are transferred by means of a Permitted Transfer must, as a condition precedent to the validity of such transfer, acknowledge in writing to the Corporation that such person is bound by the provisions of this Agreement and that the transferred shares are subject to (i) the Repurchase Right, (ii) the First Refusal Right and (iii) the Market Stand-Off, to the same extent such shares would be so subject if retained by Optionee.

          3. Market Stand-Off.

               (a) In connection with any underwritten public offering by the Corporation of its equity securities pursuant to an effective registration statement filed under the 1933 Act, including the Corporation’s initial public offering, Owner shall not sell, make any short sale of, loan, hypothecate, pledge, grant any option for the purchase of, or otherwise dispose or transfer for value or otherwise agree to engage in any of the foregoing transactions with respect to, any Purchased Shares without the prior written consent of the Corporation or its underwriters. Such restriction (the “Market Stand-Off’) shall be in effect for such period of time from and after the effective date of the final prospectus for the offering as may be requested by the Corporation or such underwriters. In no event, however, shall such period exceed one hundred eighty (180) days and the Market Stand-Off shall in all events terminate two (2) years after the effective date of the Corporation’s initial public offering.

               (b) Owner shall be subject to the Market Stand-Off provided and only if the officers and directors of the Corporation are also subject to similar restrictions.

               (c) Any new, substituted or additional securities which are by reason of any Recapitalization or Reorganization distributed with respect to the Purchased Shares shall be immediately subject to the Market Stand-Off, to the same extent the Purchased Shares are at such time covered by such provisions.

               (d) In order to enforce the Market Stand-Off, the Corporation may impose stop-transfer instructions with respect to the Purchased Shares until the end of the applicable stand-off period.

     D. REPURCHASE RIGHT

          1. Grant. The Corporation is hereby granted the right (the “Repurchase Right”), exercisable at any time during the sixty (60)-day period following the date Optionee ceases for any reason to remain in Service or (if later) during the sixty (60)-day period following the execution date of this Agreement, to repurchase at the Exercise Price any or all of the Purchased Shares in which Optionee is not, at the time of his or her cessation of Service, vested in accordance with the Vesting Schedule applicable to those shares or the special vesting acceleration provisions of Paragraph D.6 of this Agreement (such shares to be hereinafter referred to as the “Unvested Shares”).

          2. Exercise of the Repurchase Right. The Repurchase Right shall be exercisable by written notice delivered to each Owner of the Unvested Shares prior to the expiration of the sixty (60)-day exercise period. The notice shall indicate the number of Unvested Shares to be repurchased and the date on which the repurchase is to be effected, such

date to be not more than thirty (30) days after the date of such notice. The certificates representing the Unvested Shares to be repurchased shall be delivered to the Corporation on or before the close of business on the date specified for the repurchase. Concurrently with the receipt of such stock certificates, the Corporation shall pay to Owner, in cash or cash equivalents (including the cancellation of any purchase-money indebtedness), an amount equal to the Exercise Price previously paid for the Unvested Shares which are to be repurchased from Owner.

          3. Termination of the Repurchase Right. The Repurchase Right shall terminate with respect to any Unvested Shares for which it is not timely exercised under Paragraph D.2. In addition, the Repurchase Right shall terminate and cease to be exercisable with respect to any and all Purchased Shares in which Optionee vests in accordance with the Vesting Schedule. All Purchased Shares as to which the Repurchase Right lapses shall, however, remain subject to (i) the First Refusal Right and (ii) the Market Stand-Off.

          4. Aggregate Vesting Limitation. If the Option is exercised in more than one increment so that Optionee is a party to one or more other Stock Purchase Agreements (the “Prior Purchase Agreements”) which are executed prior to the date of this Agreement, then the total number of Purchased Shares as to which Optionee shall be deemed to have a fully-vested interest under this Agreement and all Prior Purchase Agreements shall not exceed in the aggregate the number of Purchased Shares in which Optionee would otherwise at the time be vested, in accordance with the Vesting Schedule, had all the Purchased Shares (including those acquired under the Prior Purchase Agreements) been acquired exclusively under this Agreement.

          5. Recapitalization. Any new, substituted or additional securities or other property (including cash paid other than as a regular cash dividend) which is by reason of any Recapitalization distributed with respect to the Purchased Shares shall be immediately subject to the Repurchase Right and any escrow requirements hereunder, but only to the extent the Purchased Shares are at the time covered by such right or escrow requirements. Appropriate adjustments to reflect such distribution shall be made to the number and/or class of Purchased Shares subject to this Agreement and to the price per share to be paid upon the exercise of the Repurchase Right in order to reflect the effect of any such Recapitalization upon the Corporation’s capital structure; provided, however, that the aggregate purchase price shall remain the same.

          6. Corporate Transaction.

               (a) The Repurchase Right shall automatically terminate in its entirety, and all the Purchased Shares shall vest in full, immediately prior to the consummation of any Corporate Transaction, except to the extent the Repurchase Right is to be assigned to the successor entity in such Corporate Transaction.

               (b) To the extent the Repurchase Right remains in effect following a Corporate Transaction, such right shall apply to any new securities or other property (including any cash payments) received in exchange for the Purchased Shares in consummation of the Corporate Transaction, but only to the extent the Purchased Shares are at the time covered by such right. Appropriate adjustments shall be made to the price per share payable upon exercise of the Repurchase Right to reflect the effect of the Corporate Transaction upon the Corporation’s

capital structure; provided, however, that the aggregate purchase price shall remain the same. The new securities or other property (including any cash payments) issued or distributed with respect to the Purchased Shares in consummation of the Corporate Transaction shall be immediately deposited in escrow with the Corporation (or the successor entity) and shall not be released from escrow until Optionee vests in such securities or other property in accordance with the same Vesting Schedule in effect for the Purchased Shares.

               (c) The Repurchase Right shall automatically lapse in its entirety, and all the Purchased Shares shall immediately vest in full, upon an Involuntary Termination of Optionee’s Service within twelve (12) months following the effective date of a Corporate Transaction in which the Repurchase Right does not otherwise terminate pursuant to Paragraph D.6(a) above.

     E. RIGHT OF FIRST REFUSAL

          1. Grant. The Corporation is hereby granted the right of first refusal (the “First Refusal Right”), exercisable in connection with any proposed transfer of the Purchased Shares in which Optionee has vested in accordance with the provisions of Article D. For purposes of this Article E, the term “transfer” shall include any sale, assignment, pledge, encumbrance or other disposition of the Purchased Shares intended to be made by Owner, but shall not include any Permitted Transfer.

          2. Notice of Intended Disposition. In the event any Owner of Purchased Shares in which Optionee has vested desires to accept a bona fide third-party offer for the transfer of any or all of such shares (the Purchased Shares subject to such offer to be hereinafter referred to as the “Target Shares”), Owner shall promptly (i) deliver to the Corporation written notice (the “Disposition Notice”) of the terms of the offer, including the purchase price and the identity of the third-party offeror, and (ii) provide satisfactory proof that the disposition of the Target Shares to such third-party offeror would not be in contravention of the provisions set forth in Articles B and C.

          3. Exercise of the First Refusal Right. The Corporation shall, for a period of twenty-five (25) days following receipt of the Disposition Notice, have the right to repurchase any or all of the Target Shares subject to the Disposition Notice upon the same terms as those specified therein or upon such other terms (not materially different from those specified in the Disposition Notice) to which Owner consents. Such right shall be exercisable by delivery of written notice (the “Exercise Notice”) to Owner prior to the expiration of the twenty-five (25)- day exercise period. If such right is exercised with respect to all the Target Shares, then the Corporation shall effect the repurchase of such shares, including payment of the purchase price, not more than five (5) business days after delivery of the Exercise Notice; and at such time the certificates representing the Target Shares shall be delivered to the Corporation.

          Should the purchase price specified in the Disposition Notice be payable in property other than cash or evidences of indebtedness, the Corporation shall have the right to pay the purchase price in the form of cash equal in amount to the value of such property. If Owner and the Corporation cannot agree on such cash value within ten (10) days after the Corporation’s receipt of the Disposition Notice, the valuation shall be made by an appraiser of recognized

standing selected by Owner and the Corporation or, if they cannot agree on an appraiser within twenty (20) days after the Corporation’s receipt of the Disposition Notice, each shall select an appraiser of recognized standing and the two (2) appraisers shall designate a third appraiser of recognized standing, whose appraisal shall be determinative of such value. The cost of such appraisal shall be shared equally by Owner and the Corporation. The closing shall then be held on the later of (i) the fifth (5th) business day following delivery of the Exercise Notice or (ii) the fifth (5th) business day after such valuation shall have been made.

          4. Non-Exercise of the First Refusal Right. In the event the Exercise Notice is not given to Owner prior to the expiration of the twenty-five (25)-day exercise period, Owner shall have a period of thirty (30) days thereafter in which to sell or otherwise dispose of the Target Shares to the third-party offeror identified in the Disposition Notice upon terms (including the purchase price) no more favorable to such third-party offeror than those specified in the Disposition Notice; provided, however, that any such sale or disposition must not be effected in contravention of the provisions of Articles B and C. The third-party offeror shall acquire the Target Shares subject to the First Refusal Right, and the acquired shares shall remain subject to the provisions of Article B and Paragraph C.3. In the event Owner does not effect such sale or disposition of the Target Shares within the specified thirty (30)-day period, the First Refusal Right shall continue to be applicable to any subsequent disposition of the Target Shares by Owner until such right lapses.

          5. Partial Exercise of the First Refusal Right. In the event the Corporation makes a timely exercise of the First Refusal Right with respect to a portion, but not all, of the Target Shares specified in the Disposition Notice, Owner shall have the option, exercisable by written notice to the Corporation delivered within five (5) business days after Owner’s receipt of the Exercise Notice, to effect the sale of the Target Shares pursuant to either of the following alternatives:

               (i) sale or other disposition of all the Target Shares to the third-party offeror identified in the Disposition Notice, but in full compliance with the requirements of Paragraph E.4, as if the Corporation did not exercise the First Refusal Right; or

               (ii) sale to the Corporation of the portion of the Target Shares which the Corporation has elected to purchase, such sale to be effected in substantial conformity with the provisions of Paragraph E.3. The First Refusal Right shall continue to be applicable to any subsequent disposition of the remaining Target Shares until such right lapses.

          Owner’s failure to deliver timely notification to the Corporation shall be deemed to be an election by Owner to sell the Target Shares pursuant to alternative (i) above.

          6. Recapitalization/Reorganization.

               (a) Any new, substituted or additional securities or other property which is by reason of any Recapitalization distributed with respect to the Purchased Shares shall

be immediately subject to the First Refusal Right, but only to the extent the Purchased Shares are at the time covered by such right.

               (b) In the event of a Reorganization, the First Refusal Right shall remain in full force and effect and shall apply to the new capital stock or other property received in exchange for the Purchased Shares in consummation of the Reorganization, but only to the extent the Purchased Shares are at the time covered by such right.

          7. Lapse. The First Refusal Right shall lapse upon the earliest to occur of (i) the first date on which shares of the Common Stock are held of record by more than five hundred (500) persons, (ii) a determination is made by the Board that a public market exists for the outstanding shares of Common Stock or (iii) a firm commitment underwritten public offering, pursuant to an effective registration statement under the 1933 Act, covering the offer and sale of the Common Stock in the aggregate amount of at least ten million dollars ($10,000,000). However, the Market Stand-Off shall continue to remain in full force and effect following the lapse of the First Refusal Right.

     F. SPECIAL TAX ELECTION

          The acquisition of the Purchased Shares may result in adverse tax consequences which may be avoided or mitigated by filing an election under Code Section 83(b). Such election must be filed within thirty (30) days after the date of this Agreement. A description of the tax consequences applicable to the acquisition of the Purchased Shares and the form for making the Code Section 83(b) election are set forth in Exhibit II. OPTIONEE SHOULD CONSULT WITH HIS OR HER TAX ADVISOR TO DETERMINE THE TAX CONSEQUENCES OF ACQUIRING THE PURCHASED SHARES AND THE ADVANTAGES AND DISADVANTAGES OF FILING THE CODE SECTION 83(b) ELECTION. OPTIONEE ACKNOWLEDGES THAT IT IS OPTIONEE’S SOLE RESPONSIBILITY, AND NOT THE CORPORATION’S, TO FILE A TIMELY ELECTION UNDER CODE SECTION 83(b), EVEN IF OPTIONEE REQUESTS THE CORPORATION OR ITS REPRESENTATIVES TO MAKE THIS FILING ON HIS OR HER BEHALF.

     G. GENERAL PROVISIONS

          1. Assignment. The Corporation may assign the Repurchase Right and/or the First Refusal Right to any person or entity selected by the Board, including (without limitation) one or more stockholders of the Corporation. If the assignee of the Repurchase Right is other than (i) a wholly owned subsidiary of the Corporation or (ii) the parent corporation owning one hundred percent (100%) of the Corporation’s outstanding capital stock, then such assignee must make a cash payment to the Corporation, upon the assignment of the Repurchase Right, in an amount equal to the excess (if any) of (i) the Fair Market Value of the Purchased Shares at the time subject to the assigned Repurchase Right over (ii) the aggregate repurchase price payable for the Purchased Shares.

          2. No Employment or Service Contract. Nothing in this Agreement or in the Plan shall confer upon Optionee any right to continue in Service for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Corporation (or any

Parent or Subsidiary employing or retaining Optionee) or of Optionee, which rights are hereby expressly reserved by each, to terminate Optionee’s Service at any time for any reason, with or without cause.

          3. Notices. Any notice required to be given under this Agreement shall be in writing and shall be deemed effective upon personal delivery or upon deposit in the U.S. mail registered or certified, postage prepaid and properly addressed to the party entitled to such notice at the address indicated below such party’s signature line on this Agreement or at such other address as such party may designate by ten (10) days advance written notice under this paragraph to all other parties to this Agreement.

          4. No Waiver. The failure of the Corporation in any instance to exercise the Repurchase Right or the First Refusal Right shall not constitute a waiver of any other repurchase rights and/or rights of first refusal that may subsequently arise under the provisions of this Agreement or any other agreement between the Corporation and Optionee. No waiver of any breach or condition of this Agreement shall be deemed to be a waiver of any other or subsequent breach or condition, whether of like or different nature.

          5. Cancellation of Shares. If the Corporation shall make available, at the time and place and in the amount and form provided in this Agreement, the consideration for the Purchased Shares to be repurchased in accordance with the provisions of this Agreement, then from and after such time, the person from whom such shares are to be repurchased shall no longer have any rights as a holder of such shares (other than the right to receive payment of such consideration in accordance with this Agreement). Such shares shall be deemed purchased in accordance with the applicable provisions hereof, and the Corporation shall be deemed the owner and holder of such shares, whether or not the certificates therefor have been delivered as required by this Agreement.

     H. MISCELLANEOUS PROVISIONS

          1. Optionee Undertaking. Optionee hereby agrees to take whatever additional action and execute whatever additional documents the Corporation may deem necessary or advisable in order to carry out or effect one or more of the obligations or restrictions imposed on either Optionee or the Purchased Shares pursuant to the provisions of this Agreement.

          2. Agreement is Entire Contract. This Agreement constitutes the entire contract between the parties hereto with regard to the subject matter hereof. This Agreement is made pursuant to the provisions of the Plan and shall in all respects be construed in conformity with the terms of the Plan.

          3. Governing Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of California without resort to that State’s conflict-of-laws rules.

          4. Counterparts. This Agreement may be executed in counterparts, each of which shall be deemed to be an original, but all of which together shall constitute one and the same Instrument.

          5. Successors and Assigns. The provisions of this Agreement shall inure to the benefit of, and be binding upon, the Corporation and its successors and assigns and upon Optionee, Optionee’s permitted assigns and the legal representatives, heirs and legatees of Optionee’s estate, whether or not any such person shall have become a party to this Agreement and have agreed in writing to join herein and be bound by the terms hereof.

          IN WITNESS WHEREOF, the parties have executed this Agreement on the day and year first indicated above.

SPOUSAL ACKNOWLEDGMENT

          The undersigned spouse of Optionee has read and hereby approves the foregoing Stock Purchase Agreement. In consideration of the Corporation’s granting Optionee the right to acquire the Purchased Shares in accordance with the terms of such Agreement, the undersigned hereby agrees to be irrevocably bound by all the terms of such Agreement, including (without limitation) the right of the Corporation (or its assigns) to purchase any Purchased Shares in which Optionee is not vested at time of his or her cessation of Service.

EXHIBIT I

ASSIGNMENT SEPARATE FROM CERTIFICATE

     FOR VALUE RECEIVED ___hereby sell(s), assign(s) and transfer(s) unto Energy Recovery, Inc. (the “Corporation”), ___ (___) shares of the Common Stock of the Corporation standing in his or her name on the books of the Corporation represented by Certificate No. ___herewith and do(es) hereby irrevocably constitute and appoint ___Attorney to transfer the said stock on the books of the Corporation with full power of substitution in the premises.

Dated: __________________

		Signature:

Instruction: Please do not fill in any blanks other than the signature line. Please sign exactly as you would like your name to appear on the issued stock certificate. The purpose of this assignment is to enable the Corporation to exercise the Repurchase Right without requiring additional signatures on the part of Optionee.

EXHIBIT II

FEDERAL INCOME TAX CONSEQUENCES AND
SECTION 83(b) TAX ELECTION

          II. Federal Income Tax Consequences and Section 83(b) Election For Exercise of Non-Statutory Option. If the Purchased Shares are acquired pursuant to the exercise of a Non-Statutory Option, as specified in the Grant Notice, then under Code Section 83, the excess of the Fair Market Value of the Purchased Shares on the date any forfeiture restrictions applicable to such shares lapse over the Exercise Price paid for such shares will be reportable as ordinary income on the lapse date. For this purpose, the term “forfeiture restrictions” includes the right of the Corporation to repurchase the Purchased Shares pursuant to the Repurchase Right. However, Optionee may elect under Code Section 83(b) to be taxed at the time the Purchased Shares are acquired, rather than when and as such Purchased Shares cease to be subject to such forfeiture restrictions. Such election must be filed with the Internal Revenue Service within thirty (30) days after the date of the Agreement. Even if the Fair Market Value of the Purchased Shares on the date of the Agreement equals the Exercise Price paid (and thus no tax is payable), the election must be made to avoid adverse tax consequences in the future. The form for making this election is attached as part of this exhibit. FAILURE TO MAKE THIS FILING WITHIN THE APPLICABLE THIRTY (30)-DAY PERIOD WILL RESULT IN THE RECOGNITION OF ORDINARY INCOME BY OPTIONEE AS THE FORFEITURE RESTRICTIONS LAPSE.

          III. Federal Income Tax Consequences and Conditional Section 83(h) Election For Exercise of Incentive Option. If the Purchased Shares are acquired pursuant to the exercise of an Incentive Option, as specified in the Grant Notice, then the following tax principles shall be applicable to the Purchased Shares:

               (i) For regular tax purposes, no taxable income will be recognized at the time the Option is exercised.

               (ii) The excess of (a) the Fair Market Value of the Purchased Shares on the date the Option is exercised or (if later) on the date any forfeiture restrictions applicable to the Purchased Shares lapse over (b) the Exercise Price paid for the Purchased Shares will be includible in Optionee’s taxable income for alternative minimum tax purposes.

               (iii) If Optionee makes a disqualifying disposition of the Purchased Shares, then Optionee will recognize ordinary income in the year of such disposition equal in amount to the excess of (a) the Fair Market Value of the Purchased Shares on the date the Option is exercised or (if later) on the date any forfeiture restrictions applicable to the Purchased Shares lapse over (b) the Exercise Price paid for the Purchased Shares. Any additional gain recognized upon the disqualifying disposition will be either short-term or long-term capital gain depending upon the period for which the Purchased Shares are held prior to the disposition.

               (iv) For purposes of the foregoing, the term “forfeiture restrictions” will include the right of the Corporation to repurchase the Purchased Shares pursuant to the Repurchase Right. The term “disqualifying disposition” means any sale or other disposition¹ of the Purchased Shares within two (2) years after the Grant Date or within one (1) year after the exercise date of the Option.

               (v) In the absence of final Treasury Regulations relating to Incentive Options, it is not certain whether Optionee may, in connection with the exercise of the Option for any Purchased Shares at the time subject to forfeiture restrictions, file a protective election under Code Section 83(b) which would limit (a) Optionee’s alternative minimum taxable income upon exercise and (b) Optionee’s ordinary income upon a disqualifying disposition to the excess of the Fair Market Value of the Purchased Shares on the date the Option is exercised over the Exercise Price paid for the Purchased Shares. Accordingly, such election if properly filed will only be allowed to the extent the final Treasury Regulations permit such a protective election. Page 2 of the attached form for making the election should be filed with any election made in connection with the exercise of an Incentive Option.

SECTION 83(b) ELECTION

          This statement is being made under Section 83(b) of the Internal Revenue Code, pursuant to Treas. Reg. Section 1.83-2.

(1)		The taxpayer who performed the services is:
		Name: Address: Taxpayer Ident. No.:
(2)		The property with respect to which the election is being made is                      shares of the common stock of Energy Recovery, Inc.
(3)		The property was issued on                     , 2004.
(4)		The taxable year in which the election is being made is the calendar year 2004.
(5)		The property is subject to a repurchase right pursuant to which the issuer has the right to acquire the property at the original purchase price if for any reason taxpayer’s service with the issuer terminates. The issuer’s repurchase right lapses in a series of annual and monthly installments over a four (4)-year period ending on                     , 200     .
(6)		The fair market value at the time of transfer (determined without regard to any restriction other than a restriction which by its terms will never lapse) is $                     per share.
(7)		The amount paid for such property is $                     per share.
(8)		A copy of this statement was furnished to Energy Recovery, Inc. for whom taxpayer rendered the services underlying the transfer of property.
(9)		This statement is executed on                      , 2004.

Spouse (if any)				Taxpayer

This election must be filed with the Internal Revenue Service Center with which taxpayer files his or her Federal income tax returns and must be made within thirty (30) days after the execution date of the Stock Purchase Agreement. This filing should be made by registered or certified mail, return receipt requested. Optionee must retain two (2) copies of the completed form for filing with his or her Federal and state tax returns for the current tax year and an additional copy for his or her records.

          The property described in the above Section 83(b) election is comprised of shares of common stock acquired pursuant to the exercise of an incentive stock option under Section 422 of the Internal Revenue Code (the “Code”). Accordingly, it is the intent of the Taxpayer to utilize this election to achieve the following tax results:

          1. The purpose of this election is to have the alternative minimum taxable income attributable to the purchased shares measured by the amount by which the fair market value of such shares at the time of their transfer to the Taxpayer exceeds the purchase price paid for the shares. In the absence of this election, such alternative minimum taxable income would be measured by the spread between the fair market value of the purchased shares and the purchase price which exists on the various lapse dates in effect for the forfeiture restrictions applicable to such shares. The election is to be effective to the full extent permitted under the Code.

          2. Section 421(a)(l) of the Code expressly excludes from income any excess of the fair market value of the purchased shares over the amount paid for such shares. Accordingly, this election is also intended to be effective in the event there is a “disqualifying disposition” of the shares, within the meaning of Section 421(b) of the Code, which would otherwise render the provisions of Section 83(a) of the Code applicable at that time. Consequently, the Taxpayer hereby elects to have the amount of disqualifying disposition income measured by the excess of the fair market value of the purchased shares on the date of transfer to the Taxpayer over the amount paid for such shares. Since Section 421 (a) presently applies to the shares which are the subject of this Section 83(b) election, no taxable income is actually recognized for regular tax purposes at this time, and no income taxes are payable, by the Taxpayer as a result of this election.

THIS PAGE 2 IS TO BE ATTACHED TO ANY SECTION 83(b) ELECTION FILED IN CONNECTION WITH THE EXERCISE OF AN INCENTIVE STOCK OPTION UNDER THE FEDERAL TAX LAWS.

APPENDIX

          The following definitions shall be in effect under the Agreement:

          A. Agreement shall mean this Stock Purchase Agreement.

          B. Board shall mean the Corporation’s Board of Directors.

          C. Code shall mean the Internal Revenue Code of 1986, as amended.

          D. Common Stock shall mean the Corporation’s common stock.

          E. Corporate Transaction shall mean either of the following stockholder-approved transactions:

          (i) a merger or consolidation in which securities possessing more than fifty percent (50%) of the total combined voting power of the Corporation’s outstanding securities are transferred to a person or persons different from the persons holding those securities immediately prior to such transaction, or

          (ii) the sale, transfer or other disposition of all or substantially all of the Corporation’s assets in complete liquidation or dissolution of the Corporation.

          F. Corporation shall mean Energy Recovery, Inc., a Delaware corporation, and any successor corporation to all or substantially all of the assets or voting stock of Energy Recovery, Inc. which shall by appropriate action adopt the Plan.

          G. Disposition Notice shall have the meaning assigned to such term in Paragraph E.2.

          H. Exercise Notice shall have the meaning assigned to such term in Paragraph E.3.

          I. Exercise Price shall have the meaning assigned to such term in Paragraph A.1.

          J. Fair Market Value of a share of Common Stock on any relevant date, prior to the initial public offering of the Common Stock, shall be determined by the Plan Administrator after taking into account such factors as it shall deem appropriate.

          K. First Refusal Right shall mean the right granted to the Corporation in accordance with Article E.

          L. Grant Date shall have the meaning assigned to such term in Paragraph A.1.

          M. Grant Notice shall mean the Notice of Grant of Stock Option pursuant to which Optionee has been informed of the basic terms of the Option.

          N. Incentive Option shall mean an option which satisfies the requirements of Code Section 422.

          O. Involuntary Termination shall mean the termination of Optionee’s Service which occurs by reason of:

          (i) Optionee’s involuntary dismissal or discharge by the Corporation for reasons other than Misconduct, or

          (ii) Optionee’s voluntary resignation following (A) a change in his or her position with the Corporation which materially reduces his or her level of responsibility, (B) a reduction in Optionee’s level of compensation (including base salary, fringe benefits and target bonuses under any corporate-performance based bonus or incentive programs) by more than fifteen percent (15%) or (C) a relocation of Optionee’s place of employment by more than fifty (50) miles, provided and only if such change, reduction or relocation is effected by the Corporation without Optionee’s consent.

          P. Market Stand-Off shall mean the market stand-off restriction specified in Paragraph C.3.

          Q. Misconduct shall mean the commission of any act of fraud, embezzlement or dishonesty by Optionee, any unauthorized use or disclosure by Optionee of confidential information or trade secrets of the Corporation (or any Parent or Subsidiary), or any other intentional misconduct by Optionee adversely affecting the business or affairs of the Corporation (or any Parent or Subsidiary) in a material manner. The foregoing definition shall not be deemed to be inclusive of all the acts or omissions which the Corporation (or any Parent or Subsidiary) may consider as grounds for the dismissal or discharge of Optionee or any other individual in the Service of the Corporation (or any Parent or Subsidiary).

          R. 1933 Act shall mean the Securities Act of 1933, as amended.

          S. 1934 Act shall mean the Securities Exchange Act of 1934, as amended.

          T. Non-Statutory Option shall mean an option not intended to satisfy the requirements of Code Section 422.

          U. Option shall have the meaning assigned to such term in Paragraph A.1.

          V. Option Agreement shall mean all agreements and other documents evidencing the Option.

          W. Optionee shall mean the person to whom the Option is granted under the Plan.

          X. Owner shall mean Optionee and all subsequent holders of the Purchased Shares who derive their chain of ownership through a Permitted Transfer from Optionee.

          Y. Parent shall mean any corporation (other than the Corporation) in an unbroken chain of corporations ending with the Corporation, provided each corporation in the unbroken chain (other than the Corporation) owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

          Z. Permitted Transfer shall mean (i) a gratuitous transfer of the Purchased Shares, provided and only if Optionee obtains the Corporation’s prior written consent to such transfer, (ii) a transfer of title to the Purchased Shares effected pursuant to Optionee’s will or the laws of intestate succession following Optionee’s death or (iii) a transfer to the Corporation in pledge as security for any purchase-money indebtedness incurred by Optionee in connection with the acquisition of the Purchased Shares.

          AA. Plan shall mean the Corporation’s 2004 Stock Option/Stock Issuance Plan.

          BB. Plan Administrator shall mean either the Board or a committee of the Board acting in its capacity as administrator of the Plan.

          CC. Prior Purchase Agreement shall have the meaning assigned to such term in Paragraph D.4.

          DD. Purchased Shares shall have the meaning assigned to such term in Paragraph A.1.

          EE. Recapitalization shall mean any stock split, stock dividend, recapitalization, combination of shares, exchange of shares or other change affecting the Corporation’s outstanding Common Stock as a class without the Corporation’s receipt of consideration.

          FF. Reorganization shall mean any of the following transactions:

          (i) a merger or consolidation in which the Corporation is not the surviving entity,

          (ii) a sale, transfer or other disposition of all or substantially all of the Corporation’s assets,

          (iii) a reverse merger in which the Corporation is the surviving entity but in which the Corporation’s outstanding voting securities are transferred

in whole or in part to a person or persons different from the persons holding those securities immediately prior to the merger, or

          (iv) any transaction effected primarily to change the state in which the Corporation is incorporated or to create a holding company structure.

          GG. Repurchase Right shall mean the right granted to the Corporation in accordance with Article D.

          HH. SEC shall mean the Securities and Exchange Commission.

          II. Service shall mean the Optionee’s performance of services for the Corporation (or any Parent or Subsidiary) in the capacity of an employee, subject to the control and direction of the employer entity as to both the work to be performed and the manner and method of performance, a non-employee member of the board of directors or an independent consultant.

          JJ. Subsidiary shall mean any corporation (other than the Corporation) in an unbroken chain of corporations beginning with the Corporation, provided each corporation (other than the last corporation) in the unbroken chain owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

          KK. Target Shares shall have the meaning assigned to such term in Paragraph E.2.

          LL. Vesting Schedule shall mean the vesting schedule specified in the Grant Notice pursuant to which the Optionee is to vest in the Option Shares in a series of installments over his or her period of Service.

          MM. Unvested Shares shall have the meaning assigned to such term in Paragraph D.1.

ADDENDUM
TO
STOCK PURCHASE AGREEMENT

          The following provisions are hereby incorporated into, and are hereby made a part of, that certain Stock Purchase Agreement (the “Purchase Agreement”) by and between Energy Recovery, Inc. (the “Corporation”) and (“Optionee”) evidencing the shares of Common Stock purchased on this date by Optionee under the Corporation’s 2004 Stock Option/Stock Issuance Plan, and such provisions shall be effective immediately. All capitalized terms in this Addendum, to the extent not otherwise defined herein, shall have the meanings assigned to such terms in the Purchase Agreement.

INVOLUNTARY TERMINATION FOLLOWING
CORPORATE TRANSACTION

	I.		TO THE EXTENT THE REPURCHASE RIGHT IS ASSIGNED TO THE SUCCESSOR CORPORATION (OR PARENT THEREOF) IN CONNECTION WITH A CORPORATE TRANSACTION, NO ACCELERATED VESTING OF THE PURCHASED SHARES SHALL OCCUR UPON SUCH CORPORATE TRANSACTION, AND THE REPURCHASE RIGHT SHALL CONTINUE TO REMAIN IN FULL FORCE AND EFFECT IN ACCORDANCE WITH THE PROVISIONS OF THE PURCHASE AGREEMENT. OPTIONEE SHALL, OVER HIS OR HER PERIOD OF SERVICE FOLLOWING THE CORPORATE TRANSACTION, CONTINUE TO VEST IN THE PURCHASED SHARES IN ONE OR MORE INSTALLMENTS IN ACCORDANCE WITH THE PROVISIONS OF THE PURCHASE AGREEMENT. HOWEVER, UPON AN INVOLUNTARY TERMINATION OF OPTIONEE’S SERVICE WITHIN SIX (6) MONTHS FOLLOWING THE CORPORATE TRANSACTION, THE REPURCHASE RIGHT SHALL TERMINATE AUTOMATICALLY, AND ALL THE PURCHASED SHARES SHALL IMMEDIATELY VEST IN FULL AT THAT TIME.
	J.		FOR PURPOSES OF THIS ADDENDUM, THE FOLLOWING DEFINITIONS SHALL BE IN EFFECT:

          An Involuntary Termination shall mean the termination of Optionee’s Service by reason of:

          1. Optionee’s involuntary dismissal or discharge by the Corporation for reasons other than for Misconduct, or

          2. Optionee’s voluntary resignation following (A) a change in his or her position with the Corporation (or Parent or Subsidiary employing Optionee) which materially reduces his or her duties and responsibilities or the level of management to which he or she reports, (B) a reduction in Optionee’s level of compensation (including base salary, fringe benefits and target

bonuses under any corporate-performance based incentive programs) by more than fifteen percent (15%) or (C) a relocation of Optionee’s place of employment by more than fifty (50) miles, provided and only if such change, reduction or relocation is effected by the Corporation without Optionee’s consent.

          Misconduct shall mean the termination of Optionee’s Service by reason of Optionee’s commission of any act of fraud, embezzlement or dishonesty, any unauthorized use or disclosure by Optionee of confidential information or trade secrets of the Corporation (or any Parent or Subsidiary), or any other intentional misconduct by Optionee adversely affecting the business or affairs of the Corporation (or any Parent or Subsidiary) in a material manner. The foregoing definition shall not be deemed to be inclusive of all the acts or omissions which the Corporation (or any Parent or Subsidiary) may consider as grounds for the dismissal or discharge of Optionee or any other individual in the Service of the Corporation (or any Parent or Subsidiary).

          IN WITNESS WHEREOF, Energy Recovery, Inc. has caused this Addendum to be executed by its duly-authorized officer as of the Effective Date specified below.

EFFECTIVE DATE:                                         ,      

ENERGY RECOVERY, INC.

2004 STOCK OPTION AGREEMENT

RECITALS

          I. The Board has adopted the Plan for the purpose of retaining the services of selected Employees, non-employee members of the Board or the board of directors of any Parent or Subsidiary and consultants and other independent advisors in the service of the Corporation (or any Parent or Subsidiary).

          A. Optionee is to render valuable services to the Corporation (or a Parent or Subsidiary), and this Agreement is executed pursuant to, and is intended to carry out the purposes of, the Plan in connection with the Corporation’s grant of an option to Optionee.

          B. All capitalized terms in this Agreement shall have the meaning assigned to them in the attached Appendix.

          NOW, THEREFORE, it is hereby agreed as follows:

          1. Grant of Option. The Corporation hereby grants to Optionee, as of the Grant Date, an option to purchase up to the number of Option Shares specified in the Grant Notice. The Option Shares shall be purchasable from time to time during the option term specified in Paragraph 2 at the Exercise Price set forth in the Grant Notice.

          2. Option Term. This option shall have a term of ten (10) years measured from the Grant Date and shall accordingly expire at the close of business on the Expiration Date, unless sooner terminated in accordance with Paragraph 5 or 6.

          3. Limited Transferability. During Optionee’s lifetime, this option shall be exercisable only by Optionee and shall not be assignable or transferable other than by will or by the laws of descent and distribution following Optionee’s death.

          4. Dates of Exercise. This option shall become exercisable for the Option Shares in one or more installments as specified in the Grant Notice. As the option becomes exercisable for such installments, those installments shall accumulate, and the option shall remain exercisable for the accumulated installments until the Expiration Date or sooner termination of the option term under Paragraph 5 or 6.

          5. Cessation of Service. The option term specified in Paragraph 2 shall terminate (and this option shall cease to be outstanding) prior to the Expiration Date should any of the following provisions become applicable:

          (a) Should Optionee cease to remain in Service for any reason (other than death, Disability or Misconduct) while this option is outstanding, then Optionee shall have a period of one (1) month (commencing with the date of such cessation of Service) during which to exercise this option, but in no event shall this option be exercisable at any time after the Expiration Date.

          (b) Should Optionee die while this option is outstanding, then the personal representative of Optionee’s estate or the person or persons to whom the option is transferred pursuant to Optionee’s will or in accordance with the laws of inheritance shall have the right to exercise this option. Such right shall lapse, and this option shall cease to be outstanding, upon the earlier of (i) the expiration of the twelve (12)-month period measured from the date of Optionee’s death or (ii) the Expiration Date.

          (c) Should Optionee cease Service by reason of Disability while this option is outstanding, then Optionee shall have a period of twelve (12) months (commencing with the date of such cessation of Service) during which to exercise this option. In no event shall this option be exercisable at any time after the Expiration Date.

Note: Exercise of this option on a date later than three (3) months following cessation of Service due to Disability will result in loss of favorable Incentive Option treatment, unless such Disability constitutes Permanent Disability. In the event that Incentive Option treatment is not available, this option will be taxed as a Non-Statutory Option upon exercise.

          (d) During the limited period of post-Service exercisability, this option may not be exercised in the aggregate for more than the number of Option Shares in which Optionee is, at the time of Optionee’s cessation of Service, vested pursuant to the Vesting Schedule specified in the Grant Notice or the special vesting acceleration provisions of Paragraph 6. Upon the expiration of such limited exercise period or (if earlier) upon the Expiration Date, this option shall terminate and cease to be outstanding for any vested Option Shares for which the option has not been exercised. To the extent Optionee is not vested in the Option Shares at the time of Optionee’s cessation of Service, this option shall immediately terminate and cease to be outstanding in respect of those shares.

          (e) Should Optionee’s Service be terminated for Misconduct, then this option shall terminate immediately and cease to remain outstanding.

          (f) In the event of a Corporate Transaction, the provisions of Paragraph 6 shall govern the period for which this option is to remain exercisable following Optionee’s cessation of Service and shall supersede any provisions to the contrary in this paragraph.

          6. Accelerated Vesting.

               (a) In the event of any Corporate Transaction, the Option Shares at the time subject to this option but not otherwise vested shall automatically vest in full so that this option shall, immediately prior to the effective date of the Corporate Transaction, become fully exercisable for all of those Option Shares and may be exercised for any or all of those Option

Shares as fully-vested shares of Common Stock. However, the Option Shares shall not vest on such an accelerated basis if and to the extent: (i) this option is assumed by the successor corporation (or parent thereof) in the Corporate Transaction and the Corporation’s repurchase rights in respect of the unvested Option Shares are assigned to such successor corporation (or parent thereof) or (ii) this option is to be replaced with a cash incentive program of the successor corporation which preserves the spread existing on the unvested Option Shares at the time of the Corporate Transaction (the excess of the Fair Market Value of those Option Shares over the Exercise Price payable for such shares) and provides for subsequent payout in accordance with the same Vesting Schedule applicable to those unvested Option Shares as set forth in the Grant Notice.

               (b) Immediately following the Corporate Transaction, this option shall terminate and cease to be outstanding, except to the extent assumed by the successor corporation (or parent thereof) in connection with the Corporate Transaction.

               (c) If this option is assumed in connection with a Corporate Transaction, then this option shall be appropriately adjusted, immediately after such Corporate Transaction, to apply to the number and class of securities which would have been issuable to Optionee in consummation of such Corporate Transaction had the option been exercised immediately prior to such Corporate Transaction, and appropriate adjustments shall also be made to the Exercise Price, provided the aggregate Exercise Price shall remain the same.

               (d) Should there occur an Involuntary Termination of Optionee’s Service within twelve (12) months following a Corporate Transaction in which the Option Shares do not otherwise vest on an accelerated basis pursuant to Paragraph 6(a), then all the Option Shares subject to this option at the time of such Involuntary Termination but not otherwise vested shall automatically vest and the Corporation’s repurchase rights in respect of those shares shall terminate so that this option shall immediately become exercisable for all the Option Shares as fully-vested shares. The option shall remain exercisable for any or all of those vested Option Shares until the earlier of (i) the Expiration Date or (ii) the expiration of the one (l)-year period measured from the date of the Involuntary Termination.

               (e) This Agreement shall not in any way affect the right of the Corporation to adjust, reclassify, reorganize or otherwise change its capital or business structure or to merge, consolidate, dissolve, liquidate or sell or transfer all or any part of its business or assets.

          7. Adjustment in Option Shares. Should any change be made to the Common Stock by reason of any stock split, stock dividend, recapitalization, combination of shares, exchange of shares or other change affecting the outstanding Common Stock as a class without the Corporation’s receipt of consideration, appropriate adjustments shall be made to (i) the total number and/or class of securities subject to this option and (ii) the Exercise Price in order to reflect such change and thereby preclude a dilution or enlargement of benefits hereundcr.

          8. Stockholder Rights. The holder of this option shall not have any stockholder rights in respect of the Option Shares until such person shall have exercised the option, paid the Exercise Price and become the record holder of the purchased shares.

                    (v) Make appropriate arrangements with the Corporation (or Parent or Subsidiary employing or retaining Optionee) for the satisfaction of all Federal, state and local income and employment tax withholding requirements applicable to the option exercise.

               (b) As soon as practical after the Exercise Date, the Corporation shall issue to or on behalf of Optionee (or any other person or persons exercising this option) a certificate for the purchased Option Shares, with the appropriate legends affixed thereto.

               (c) In no event may this option be exercised for any fractional shares.

          10. REPURCHASE RIGHTS. ALL OPTION SHARES ACQUIRED UPON THE EXERCISE OF THIS OPTION SHALL BE SUBJECT TO CERTAIN RIGHTS OF THE CORPORATION AND ITS ASSIGNS TO REPURCHASE THOSE SHARES IN ACCORDANCE WITH THE TERMS SPECIFIED IN THE PURCHASE AGREEMENT.

          11. Compliance with Laws and Regulations.

               (a) The exercise of this option and the issuance of the Option Shares upon such exercise shall be subject to compliance by the Corporation and Optionee with all applicable requirements of law relating thereto and with all applicable regulations of any stock exchange (or the Nasdaq National Market, if applicable) on which the Common Stock may be listed for trading at the time of such exercise and issuance.

               (b) The inability of the Corporation to obtain approval from any regulatory body having authority deemed by the Corporation to be necessary to the lawful issuance and sale of any Common Stock pursuant to this option shall relieve the Corporation of any liability in respect of the non-issuance or sale of the Common Stock as to which such approval shall not have been obtained. The Corporation, however, shall use its best efforts to obtain all such approvals.

          12. Successors and Assigns. Except to the extent otherwise provided in Paragraphs 3 and 6, the provisions of this Agreement shall inure to the benefit of, and be binding upon, the Corporation and its successors and assigns and Optionee, Optionee’s assigns and the legal representatives, heirs and legatees of Optionee’s estate.

          13. Notices. Any notice required to be given or delivered to the Corporation under the terms of this Agreement shall be in writing and addressed to the Corporation at its principal corporate offices. Any notice required to be given or delivered to Optionee shall be in writing and addressed to Optionee at the address indicated below Optionee’s signature line on the Grant Notice. All notices shall be deemed effective upon personal delivery or upon deposit in the U.S. mail, postage prepaid and properly addressed to the party to be notified.

          14. Construction. This Agreement and the option evidenced hereby are made and granted pursuant to the Plan and are in all respects limited by and subject to the terms of the Plan. All decisions of the Plan Administrator in respect of any question or issue arising under the

Plan or this Agreement shall be conclusive and binding on all persons having an interest in this option.

          15. Governing Law. The interpretation, performance and enforcement of this Agreement shall be governed by the laws of the State of California without resort to that State’s conflict-of-laws rules.

          16. Stockholder Approval. If the Option Shares covered by this Agreement exceed, as of the Grant Date, the number of shares of Common Stock which may be issued under the Plan as last approved by the stockholders, then this option shall be void in respect of such excess shares, unless stockholder approval of an amendment sufficiently increasing the number of shares of Common Stock issuable under the Plan is obtained in accordance with the provisions of the Plan.

          17. Additional Terms Applicable to an Incentive Option. In the event this option is designated an Incentive Option in the Grant Notice, the following terms and conditions shall also apply to the grant:

               (a) This option shall cease to qualify for favorable tax treatment as an Incentive Option if (and to the extent) this option is exercised for one or more Option Shares: (i) more than three (3) months after the date Optionee ceases to be an Employee for any reason other than death or Permanent Disability or (ii) more than twelve (12) months after the date Optionee ceases to be an Employee by reason of Permanent Disability.

               (b) This option shall not become exercisable in the calendar year in which granted if (and to the extent) the aggregate Fair Market Value (determined at the Grant Date) of the Common Stock for which this option would otherwise first become exercisable in such calendar year would, when added to the aggregate value (determined as of the respective date or dates of grant) of the Common Stock and any other securities for which one or more other Incentive Options granted to Optionee prior to the Grant Date (whether under the Plan or any other option plan of the Corporation or any Parent or Subsidiary) first become exercisable during the same calendar year, exceed One Hundred Thousand Dollars ($100,000) in the aggregate. To the extent the exercisability of this option is deferred by reason of the foregoing limitation, the deferred portion shall become exercisable in the first calendar year or years thereafter in which the One Hundred Thousand Dollar ($100,000) limitation of this Paragraph 18(b) would not be contravened, but such deferral shall in all events end immediately prior to the effective date of a Corporate Transaction in which this option is not to be assumed or an Involuntary Termination following a Corporate Transaction in which this option is assumed, whereupon the option shall become immediately exercisable as a Non-Statutory Option for the deferred portion of the Option Shares.

               (c) Should Optionee hold, in addition to this option, one or more other options to purchase Common Stock which become exercisable for the first time in the same calendar year as this option, then the foregoing limitations on the exercisability of such options as Incentive Options shall be applied on the basis of the order in which such options are granted.

     The Optionee represents that the Optionee is familiar with the terms and provisions of this Option Agreement and hereby accepts the Option subject to all of the terms and provisions thereof. The Optionee hereby agrees to accept as binding, conclusive and final all decisions or interpretations of the Board upon any questions arising under this Option Agreement. The undersigned acknowledges receipt of a copy of the Plan.

	Optionee Address:

APPENDIX

          The following definitions shall be in effect under the Agreement:

          A. Agreement shall mean this Stock Option Agreement.

          B. Board shall mean the Corporation’s Board of Directors.

          C. Code shall mean the Internal Revenue Code of 1986, as amended.

          D. Common Stock shall mean the Corporation’s common stock.

          E. Corporate Transaction shall mean either of the following stockholder-approved transactions to which the Corporation is a party:

               (i) a merger or consolidation in which securities possessing more than fifty percent (50%) of the total combined voting power of the Corporation’s outstanding securities are transferred to a person or persons different from the persons holding those securities immediately prior to such transaction, or

               (ii) the sale, transfer or other disposition of all or substantially all of the Corporation’s assets in complete liquidation or dissolution of the Corporation.

          F. Corporation shall mean Energy Recovery, Inc., a Delaware corporation, and any successor corporation to all or substantially all of the assets or voting stock of Energy Recovery, Inc. which shall by appropriate action adopt the Plan.

          G. Disability shall mean the inability of Optionee to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment and shall be determined by the Plan Administrator on the basis of such medical evidence as the Plan Administrator deems warranted under the circumstances. Disability shall be deemed to constitute Permanent Disability in the event that such Disability is expected to result in death or has lasted or can be expected to last for a continuous period of twelve (12) months or more.

          H. Employee shall mean an individual who is in the employ of the Corporation (or any Parent or Subsidiary), subject to the control and direction of the employer entity as to both the work to be performed and the manner and method of performance.

          I. Exercise Date shall mean the date on which the option shall have been exercised in accordance with Paragraph 9 of the Agreement.

          J. Exercise Price shall mean the exercise price payable per Option Share as specified in the Grant Notice.

          K. Expiration Date shall mean the date on which the option expires as specified in the Grant Notice.

          L. Fair Market Value per share of Common Stock on any relevant date shall be determined in accordance with the following provisions:

               (i) If the Common Stock is at the time traded on the Nasdaq National Market, then the Fair Market Value shall be the closing selling price per share of Common Stock on the date in question, as the price is reported by the National Association of Securities Dealers on the Nasdaq National Market. If there is no closing selling price for the Common Stock on the date in question, then the Fair Market Value shall be the closing selling price on the last preceding date for which such quotation exists.

               (ii) If the Common Stock is at the time listed on any Stock Exchange, then the Fair Market Value shall be the closing selling price per share of Common Stock on the date in question on the Stock Exchange determined by the Plan Administrator to be the primary market for the Common Stock, as such price is officially quoted in the composite tape of transactions on such exchange. If there is no closing selling price for the Common Stock on the date in question, then the Fair Market Value shall be the closing selling price on the last preceding date for which such quotation exists.

               (iii) If the Common Stock is at the time neither listed on any Stock Exchange nor traded on the Nasdaq National Market, then the Fair Market Value shall be determined by the Plan Administrator after taking into account such factors as the Plan Administrator shall deem appropriate.

          M. Grant Date shall mean the date of grant of the option as specified in the Grant Notice.

          N. Grant Notice shall mean the Notice of Grant of Stock Option accompanying the Agreement, pursuant to which Optionee has been informed of the basic terms of the option evidenced hereby.

          O. Incentive Option shall mean an option which satisfies the requirements of Code Section 422.

          P. Involuntary Termination shall mean the termination of Optionee’s Service which occurs by reason of:

               (i) Optionee’s dismissal or discharge by the Corporation for reasons other than Misconduct, or

               (ii) Optionee’s voluntary resignation following (A) a change in Optionee’s position with the Corporation (or Parent or Subsidiary employing Optionee) which materially reduces Optionee’s level of responsibility, (B) a reduction in Optionee’s level of compensation (including base salary, fringe benefits and target bonuses under any corporate-performance based bonus or incentive programs) by more than fifteen percent (15%) in the aggregate or (C) a relocation of Optionee’s place of employment by more than fifty (50) miles from

Optionee’s place of employment immediately prior to the Corporate Transaction, provided and only if such change, reduction or relocation is effected by the Corporation without Optionee’s consent.

          Q. Misconduct shall mean the commission of any act of fraud, embezzlement or dishonesty by Optionee, any unauthorized use or disclosure by Optionee of confidential information or trade secrets of the Corporation (or any Parent or Subsidiary), or any other intentional misconduct by Optionee adversely affecting the business or affairs of the Corporation (or any Parent or Subsidiary) in a material manner. The foregoing definition shall not be deemed to be inclusive of all the acts or omissions which the Corporation (or any Parent or Subsidiary) may consider as grounds for the dismissal or discharge of Optionee or any other individual in the Service of the Corporation (or any Parent or Subsidiary).

          R. 1934 Act shall mean the Securities Exchange Act of 1934, as amended.

          S. Non-Statutory Option shall mean an option not intended to satisfy the requirements of Code Section 422.

          T. Option Shares shall mean the number of shares of Common Stock subject to the option.

          U. Optionee shall mean the person to whom the option is granted as specified in the Grant Notice.

          V. Parent shall mean any corporation (other than the Corporation) in an unbroken chain of corporations ending with the Corporation, provided each corporation in the unbroken chain (other than the Corporation) owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

          W. Plan shall mean the Corporation’s 2004 Stock Option/Stock Issuance Plan.

          X. Plan Administrator shall mean either the Board or a committee of the Board acting in its capacity as administrator of the Plan.

          Y. Purchase Agreement shall mean the stock purchase agreement in substantially the form of Exhibit B to the Grant Notice.

          Z. Service shall mean the Optionee’s performance of services for the Corporation (or any Parent or Subsidiary) in the capacity of an Employee, a non-employee member of the board of directors or an independent consultant.

          AA. Stock Exchange shall mean the American Stock Exchange or the New York Stock Exchange.

          BB. Subsidiary shall mean any corporation (other than the Corporation) in an unbroken chain of corporations beginning with the Corporation, provided each corporation (other

than the last corporation) in the unbroken chain owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

          CC. Vesting Schedule shall mean the vesting schedule specified in the Grant Notice pursuant to which the Optionee is to vest in the Option Shares in a series of installments over his or her period of Service.