California Code, Water Code - WAT § 13285

(b)(1) A public water system, or its customers, shall not be responsible for remediation or treatment costs associated with MTBE, or a product that contains MTBE.  However, the public water system may, as necessary, incur MTBE remediation and treatment costs and include those costs in its customer rates and charges that are necessary to comply with drinking water standards or directives of the state board or other lawful authority.  A public water system that incurs MTBE remediation or treatment costs may seek recovery of those costs from parties responsible for the MTBE contamination, or from other available alternative sources of funds.

(2) If the public water system has included the costs of MTBE treatment and remediation in its customer rates and charges, and subsequently recovers all, or a portion of, its MTBE treatment and remediation costs from responsible parties or other available alternative sources of funds, it shall make an adjustment to its schedule of rates and charges to reflect the amount of funding received from responsible parties or other available alternative sources of funds for MTBE treatment or remediation.

(3) Paragraph (1) does not prevent the imposition of liability on any person for the discharge of MTBE if that liability is due to the conduct or status of that person independently of whether the person happens to be a customer of the public water system.