California Code, Health and Safety Code - HSC § 116366

(a) No public water system, or its customers, shall be responsible for remediation or treatment costs associated with MTBE, or a product that contains MTBE, provided, however, that the public water system shall be permitted as necessary to incur MTBE remediation and treatment costs and to include those costs in its customer rates and charges, necessary to comply with drinking water standards or directives of the State Department of Health Services or other lawful authority.  Any 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.

(b) 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.

(c) Subdivision (a) shall 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.