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By using this site, you are agreeing to security monitoring and auditing. For security purposes, and to ensure that the public service remains available to users, this government computer system employs programs to monitor network traffic to identify unauthorized attempts to upload or change information or to otherwise cause damage, including attempts to deny service to users.

Unauthorized attempts to upload information and/or change information on any portion of this site are strictly prohibited and are subject to prosecution under the Computer Fraud and Abuse Act of 1986 and the National Information Infrastructure Protection Act of 1996 (see Title 18 U.S.C. §§ 1001 and 1030).

To ensure our website performs well for all users, the SEC monitors the frequency of requests for SEC.gov content to ensure automated searches do not impact the ability of others to access SEC.gov content. We reserve the right to block IP addresses that submit excessive requests. Current guidelines limit users to a total of no more than 10 requests per second, regardless of the number of machines used to submit requests.

If a user or application submits more than 10 requests per second, further requests from the IP address(es) may be limited for a brief period. Once the rate of requests has dropped below the threshold for 10 minutes, the user may resume accessing content on SEC.gov. This SEC practice is designed to limit excessive automated searches on SEC.gov and is not intended or expected to impact individuals browsing the SEC.gov website.

Note that this policy may change as the SEC manages SEC.gov to ensure that the website performs efficiently and remains available to all users.

Note: We do not offer technical support for developing or debugging scripted downloading processes.

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2026-02-25 2026-02-25

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report Pursuant to Section 13 or 15(d) of

The Securities Exchange Act of 1934

Date of Report (date of earliest event reported): February 25, 2026

CALIFORNIA WATER SERVICE GROUP

(Exact name of Registrant as Specified in its Charter)

Delaware

(State or other jurisdiction of incorporation) 1-13883

(Commission file number) 77-0448994

(I.R.S. Employer Identification Number)

1720 North First Street San Jose, California

(Address of principal executive offices) 95112

(Zip Code)

(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:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common Shares, par value $0.01

CWT

New York Stock Exchange

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. ¨

Item 2.02. Results of Operations and Financial Condition

On February 25, 2026, California Water Service Group (the “Company”) issued a press release (a copy of which is attached hereto as Exhibit 99.1 and incorporated herein by reference) announcing its financial results for the fourth quarter and year ended December 31, 2025.

As announced, the Company will host a conference call on Thursday, February 26, 2026 at 11:00 am EDT to discuss financial results and management’s business outlook. The financial results announcement contains information about how to access the conference call and webcast. A slide presentation, which includes supplemental information relating to the Company, will be used by management during the conference call. A copy of the slide presentation is attached hereto as Exhibit 99.2 and is incorporated by reference herein. The Exhibits will be posted on the Company’s website at www.calwatergroup.com under the “Investor Relations” tab.

The information furnished pursuant to Item 2.02 of this Current Report shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 7.01. Regulation FD Disclosure

On February 25, 2026, the Company issued a press release (a copy of which is attached hereto as Exhibit 99.3 and incorporated herein by reference) announcing that has entered into a definitive agreement to purchase Nexus Water Group’s Nevada and Oregon subsidiaries.

The information furnished pursuant to Item 7.01 of this Current Report shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 8.01. Other Events

On February 25, 2026, the Company announced that it has entered into a definitive agreement to purchase Nexus Water Group’s Nevada and Oregon subsidiaries. The purchase price for the transaction is approximately $218 million, subject to certain closing adjustments. The Company will fund the acquisition with working capital and existing debt and equity facilities. The Company expects to consummate the transaction by the end of 2026, subject to customary closing conditions and regulatory approvals, including approval from the applicable public utility commissions. The transaction is expected to add approximately 36,000 equivalent residential connections across water and wastewater systems in Nevada and Oregon and increase consolidated rate base by approximately $109 million.

Forward-Looking

Statements

T