Exhibit 32.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER,
PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO SECTION 906 OF THE
SARBANES-OXLEY ACT OF 2002*

Pursuant to the requirement set forth in Rule 13a-14(b) of the Securities and Exchange Act of 1934, as amended (the “Exchange Act”), and Section 1350 of Chapter 63 of Title 18 of the United States Code, G.G. Pique, President and Chief Executive Officer of Energy Recovery, Inc. (the “Company”), and Thomas D. Willardson, Chief Financial Officer of the Company, each hereby certify that, to the best of their knowledge:

1. The Company’s Annual Report on Form 10-K for the period ended December 31, 2009, to which this Certification is attached as Exhibit 32.1 (the “Annual Report”) fully complies with the requirements of Section 13(a) or Section 15(d) of the Exchange Act, and

2. The information contained in the Annual Report fairly presents, in all material respects, the financial condition of the Company at the end of the period covered by the Annual Report and results of operations of the Company for the period covered by the Annual Report.

IN WITNESS WHEREOF, the undersigned have set their hands hereto as of the 15th day of March 2010.

/s/ G.G. Pique				/s/ Thomas D. Willardson
President and Chief Executive Officer				Chief Financial Officer
Dated: March 15, 2010				Dated: March 15, 2010