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Use these links to rapidly review the document TABLE OF CONTENTS Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 Form 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission file No. 1-13883 CALIFORNIA WATER SERVICE GROUP ( Exact name of registrant as specified in its charter ) Delaware ( State or Other Jurisdiction of Incorporation or Organization ) 1720 North First Street San Jose , California ( Address of Principal Executive Offices ) to Title of Each Class : Common Stock , $ 0.01 par value per share ( 408 ) 367-8200 ( Registrant's Telephone Number , including Area Code ) 77-0448994 ( I.R.S. Employer Identification No. ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) CWT 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 No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 of Section 15 ( d ) of the Act . Yes No 95112 ( Zip Code ) Large accelerated Filer Non - accelerated filer Name of Each Exchange on Which Registered : New York Stock Exchange 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 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 No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C.7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No