西水资源美股招股说明书(2025-10-17版)

Up to $75,000,000 Common Stock This prospectus supplement (this “Prospectus Supplement”) amends and supplements the prospectus supplement datedAugust30, 2024, and the prospectus supplement dated March21, 2025 (together, the “ATM Prospectus”). This ProspectusSupplement should be read in conjunction with the ATM Prospectus and the accompanying base prospectus dated August29, 2025,filed with the Securities and Exchange Commission as a part of our registration statement on FormS-3 (File No.333-280685) (the“Registration Statement”), relating to the offer and sale of shares of our common stock from time to time pursuant to the terms oftheAt the Market Offering Agreement dated as of August30, 2024 (the “ATM Agreement”) withH.C. Wainwright& Co., LLC (the“Sales Agent”), acting as sales agent or principal. This Prospectus Supplement is qualified by reference to the ATM Prospectus, exceptto the extent that the information herein amends or supersedes the information contained in the ATM Prospectus. This ProspectusSupplement is not complete without and may only be delivered or utilized in connection with the ATM Prospectus, and any futureamendments or supplements thereto. We are filing this Prospectus Supplement to amend the ATM Prospectusto increase the amountof shares of our common stock,$0.001 par value per share that we may offer and sell through the Sales Agent pursuant to the ATM Agreement to $75,000,000, whichdoes not include the approximately $55 million of shares that were previously sold pursuant to the ATM Agreement as of the date ofthis Prospectus Supplement. Sales of common stock, if any, under this Prospectus Supplement and the ATM Prospectus may be made in transactions that aredeemed to be “at-the-market” offerings as defined inRule415under theSecurities Act of 1933, as amended (the “Securities Act”),including sales made directly on or through NYSE American Stock Exchange ( “NYSE American”), the existing trading market forour common stock, or any other existing trading market in the Unites States for our common stock, sales made to or through a marketmaker other than on an exchange or otherwise, directly to the Sales Agent as principal, in negotiated transactions at market pricesprevailing at the time of sale or at prices related to such prevailing market prices, and/or in any other method permitted by law. TheSales Agent is not required to sell any specific number or dollar amount of shares, but will act as sales agent on a commerciallyreasonable efforts basis consistent with its normal trading and sales practices. There is no arrangement for funds to be received in anyescrow, trust or similar arrangement. Our common stock is listed on NYSE American under the symbol “WWR.” On October 16, 2025, the last reported sale price ofour common stock on the NYSE American was $2.10 per share. Investing in our common stock involves a high degree of risk. Please read “Risk Factors” beginning on pageS-6 of theATM Prospectus, as well as the risks set forth in our most recent Annual Report on Form10-K and the other reports we filewith the Securities and Exchange Commission pursuant to the Securities Exchange Act of 1934, as amended, which areincorporated by reference into this prospectus supplement and the ATM Prospectus, for a discussion of certain risks thatshould be considered in connection with an investment in our common stock. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved ofthese securities or passed upon the adequacy or accuracy of the ATM Prospectus, this prospectus supplement or theaccompanying base prospectus. Any representation to the contrary is a criminal offense. H.C. Wainwright& Co. The date of this prospectus supplement is October17, 2025.