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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ( Mark One ) Annual Report Pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 For the fiscal year ended September 30 , 2021 or Transition Report Pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 For the transition period from Commission file number : 001-38272 EVOQUA WATER TECHNOLOGIES CORP . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 210 Sixth Avenue to Pittsburgh , Pennsylvania ( Address of principal executive offices ) Title of each class : Common Stock , par value $ 0.01 per share 46-4132761 ( I.R.S. Employer Identification No. ) 15222 ( Zip Code ) Registrant's telephone number , including area code : ( 724 ) 772-0044 Securities registered pursuant to section 12 ( b ) of the act : Trading Symbol ( s ) : AQUA Name of each exchange on which registered : New York Stock Exchange Securities registered pursuant to section 12 ( g ) of the act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes No X Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes X No