POWER OF ATTORNEY

          The undersigned, as a Section 16 reporting person of Energy Recovery,
Inc. (the "Company"), hereby constitutes and appoints G.G. Pique and Thomas
Willardson, and each of them, the undersigned's true and lawful attorney-in-fact
to:

     1.   complete and execute Forms ID, 3, 4 and 5 and other forms and all
          amendments thereto as such attorney-in-fact shall in his or her
          discretion determine to be required or advisable pursuant to Section
          16 of the Securities Exchange Act of 1934 (as amended) and the rules
          and regulations promulgated thereunder, or any successor laws and
          regulations, as a consequence of the undersigned's ownership,
          acquisition or disposition of securities of the Company; and

     2.   do all acts necessary in order to file such forms with the Securities
          and Exchange Commission, any securities exchange or national
          association, the Company and such other person or agency as the
          attorney-in-fact shall deem appropriate.

          The undersigned hereby ratifies and confirms all that said
attorneys-in-fact and agents shall do or cause to be done by virtue hereof. The
undersigned acknowledges that the foregoing attorneys-in-fact, in serving in
such capacity at the request of the undersigned, are not assuming, nor is the
Company assuming, any of the undersigned's responsibilities to comply with
Section 16 of the Securities Exchange Act of 1934 (as amended).

          This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms ID, 3, 4 and 5 with respect to
the undersigned's holdings of and transactions in securities issued by the
Company, unless earlier revoked by the undersigned in a signed writing delivered
to the Company and the foregoing attorneys-in-fact.

          IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney
to be executed as of this 1st day of July, 2008.

                                        ARVARIUS AS


                                        /s/ Hans Peter Michelet
                                        ----------------------------------------
                                        (signature)

                                        Hans Peter Michelet, Director
                                        (print name and title)