Company: AWK
Filing Date: 2025-04-30
Form Type: DEFA14A
Source: 0001410636-25-000086
Chunk: 0

Company: American Water Works Company, Inc.
Filing Date: 2025-04-30
Form: DEFA14A
Chunk 0
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549
<div align='center'>______________________</div>

#### SCHEDULE 14A
<div align='center'>______________________</div>

#### Proxy Statement Pursuant to Section 14(a) of the

#### Securities Exchange Act of 1934
Filed by the Registrant ☒ Filed by a Party other than the Registrant ¨

| Check the appropriate box: |     |                                                                                 |
| ¨                          |     | Preliminary Proxy Statement                                                     |
| ¨                          |     | Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |
| ¨                          |     | Definitive Proxy Statement                                                      |
| ☒                          |     | Definitive Additional Materials                                                 |
| ¨                          |     | Soliciting Material Pursuant to § 240.14a-12                                    |

#### AMERICAN WATER WORKS COMPANY, INC.
<div align='center'>(Name of Registrant as Specified in its Charter)</div>

<div align='center'>(Name of Person(s) Filing Proxy Statement if other than the Registrant)</div>

| Payment of Filing Fee (Check the appropriate box): |     |                                                                                                     |
| ☒                                                  |     | No fee required                                                                                     |
| ¨                                                  |     | Fee paid previously with preliminary materials                                                      |
| ¨                                                  |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |

American Water Works Company, Inc., a Delaware corporation (“ American Water ” or the “ Company ”), is filing the following information with the U.S. Securities and Exchange Commission (the “ SEC ”) as definitive additional materials pursuant to Rule 14a-6(b) under the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), in connection with the solicitation of proxies for American Water’s 2025 Annual Meeting of Shareholders (the “ Annual Meeting ”), to be held virtually on Wednesday, May 14, 2025, at 10:00 a.m., Eastern time. On March 27, 2025, American Water filed a definitive proxy statement (the “ Proxy Statement ”) and a definitive form of proxy card with the SEC in connection with the 2025 Annual Meeting. The following information supplements the