Company: AWK
Filing Date: 2025-10-27
Form Type: 425
Source: 0001193125-25-250649
Chunk: 11

Company: American Water Works Company, Inc.
Filing Date: 2025-10-27
Form: 425
Chunk 11
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 registration statement and joint proxy statement/prospectus and other relevant materials to be filed with the SEC regarding the proposed merger when such materials become available. Investors and
security holders should read the registration statement and joint proxy statement/prospectus carefully when it becomes available before making any voting or investment decisions. Investors may obtain free copies of these documents from American
Water and Essential as indicated above.

No Offer or Solicitation

This Current Report on Form 8-K is not intended to, and shall not, constitute an offer to sell or
the solicitation of an offer to buy any securities, or a solicitation of any vote for approval, nor shall there be any offer or sale of securities or solicitation of any vote or approval in any jurisdiction in which such offer, solicitation or sale
would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities
Act of 1933, as amended.

6

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.

| Dated: October 27, 2025 |     | AMERICAN WATER WORKS COMPANY, INC. 
 By:                                |     | /s/ JOHN C. GRIFFITH                  |
|:------------------------|:----|:-----------------------------------|:----|:--------------------------------------|
|                         |     |                                    |     | John C. Griffith                      |
|                         |     |                                    |     | President and Chief Executive Officer |

7

Exhibit 2.1

EXECUTION VERSION

AGREEMENT AND PLAN OF MERGER

by and among

AMERICAN WATER WORKS COMPANY, INC.,

ALPHA MERGER SUB, INC.

and

ESSENTIAL UTILITIES, INC.

Dated as of October 26, 2025

TABLE OF CONTENTS

|                                                                      |     |                                                               |     | Page |    |
| ARTICLE I                                                            |     |                                                               |     |      |    |
| THE MERGER                                                           |     |                                                               |     |      |    |
| Section 1.1                                                          |     | The Merger                                                    |     |      |  2 |
| Section 1.2                                                          |     | Closing                                                       |     |      |  2 |
| Section 1.3                                                          |