UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report Pursuant to Section 13or 15(d) of The Securities Exchange Act of 1934

Date of Report (date of earliest event reported): January 28, 2026

CALIFORNIA WATER SERVICE GROUP

(Exact name of Registrant as Specified in its Charter)

(408) 367-8200

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined by Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

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. ¨

On January 28, 2026, California Water Service Group issued a press release (a copy of which is attached hereto as Exhibit 99.1 and incorporated herein by reference) announcing the declaration of a quarterly dividend of $0.3350 per common share. The quarterly dividend will be payable on February 20, 2026 to stockholders of record as of the close of business on February 9, 2026.

(d) Exhibits.

We hereby file the following exhibit with this report:

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Exhibit 99.1

January 28, 2026

For immediate release

California Water Service Group Board of Directors Announces 59^th^ Annual

Dividend Increase and Declares 324th Consecutive Quarterly Dividend

SANJOSE, Calif., January 28, 2026 —To kick off its Centennial Celebration, California Water Service Group (NYSE:CWT) declared its 324^th^ consecutive quarterly dividend in the amount of $0.3350 per common share, payable on February 20, 2026, to stockholders of record as of the close of business on February 9, 2026. The quarterly dividend increase follows the Board of Directors’ announcement of its intent to increase the annual dividend by 8% or $0.10 per common share to $1.34, compared to the $1.20 annual dividend and $0.04 special dividend paid in 2025.

“One of the many things we’ll be celebrating during our 100^th^ anniversary is the value we’ve delivered to stockholders throughout our history. I’m proud of our strong dividend track record, and I know it’s something that is important to our stockholders,” said Chairman and Chief Executive Officer Martin A. Kropelnicki.

About California Water Service Group

California Water Service Group is the parent company of regulated utilities California Water Service, Hawaii Water Service, New Mexico Water Service, and Washington Water Service, as well as Texas Water Service, a utility holding company. Together, these companies provide regulated and non-regulated water and wastewater service to more than 2.1 million people in California, Hawaii, New Mexico, Washington, and Texas. California Water Service Group’s common stock trades on the New York Stock Exchange under the symbol “CWT.” Additional information is available online at www.calwatergroup.com.

Forward Looking Statements

This news release contains forward-looking statements within themeaning established by the Private Securities Litigation Reform Act of 1995 (“PSLRA”). The forward-looking statements areintended to qualify under provisions of the federal securities laws for “safe harbor” treatment established by the PSLRA.Forward-looking statements in this news release are based on currently available information, expectations, estimates, assumptions andprojections, and our management’s beliefs, assumptions, judgments and expectations about us, the water utility industry and generaleconomic conditions. These statements are not statements of historical fact. When used in our documents, statements that are not historicalin nature, including words like will, would, expects, intends, plans, believes, may, could, estimates, assumes, anticipates, projects,progress, predicts, hopes, targets, forecasts, should, seeks or variations of these words or similar expressions are intended to identifyforward-looking statements. Examples of forward-looking statements in this news release include, but are not limited to, statements describingGroup’s expectations regarding the annual dividend, which remains subject to the Board’s approval and declaration of subsequentquarterly dividends during the year. Forward-looking statements are not guarantees of future performance. They are based on numerous assumptionsthat we believe are reasonable, but they are open to a wide range of uncertainties and business risks. Consequently, actual results oroutcomes may vary materially from what is contained in a forward-looking statement. Factors that may cause actual results or outcomesto be different than those expected or anticipated include but are not limited to those described under the section entitled “RiskFactors” and elsewhere in our most recent Annual Report on Form 10-K, our subsequent Quarterly Reports on Form 10-Q and our otherSecurities and Exchange Commission filings. In light of these risks, uncertainties and assumptions, investors are cautioned not to placeundue reliance on forward-looking statements, which speak only as of the date of this news release. We are not under any obligation, andwe expressly disclaim any obligation, to update or alter any forward-looking statements, whether as a result of new information, futureevents or otherwise.

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Contact

James P. Lynch

408-367-8200

Shannon Dean

sdean@calwater.com

408-367-8243