Company: AWK
Filing Date: 2025-10-27
Form Type: 425
Source: 0001193125-25-250649
Chunk: 0

Company: American Water Works Company, Inc.
Filing Date: 2025-10-27
Form: 425
Chunk 0
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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): October 26, 2025 American Water Works Company, Inc. (Exact name of registrant as specified in its charter) Commission File Number: 001-34028

| Delaware                     |     | 51-0063696         |
| (State or other jurisdiction 
 of incorporation)            |     | -IRS Employer      
 Identification No. |

1 Water Street Camden, NJ 08102-1658 (Address of principal executive offices, including zip code) (856) 955-4001 (Registrant’s telephone number, including area code) Check the appropriate box below if the Form 8-Kfiling 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  |     | Name of Each Exchange   
 on Which Registered     |
| Common stock, par value $0.01 per share |     | AWK     |     | New York Stock Exchange |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR 230.405) or Rule 12b-2of the Securities Exchange Act of 1934 (17 CFR 240.12b-2). 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. ☐