(a) A public water system shall comply with the requirements of this section within 30 days after it is first informed of a confirmed detection of a contaminant found in drinking water delivered by the public water system for human consumption that is in excess of a maximum contaminant level, a notification level, or a response level established by the department.

1. (1) If the public water system is a wholesale water system, then the person operating the wholesale water system shall notify the wholesale water system’s governing body and the water systems that are directly supplied with that drinking water. If the wholesale water system is a water company regulated by the California Public Utilities Commission, then the wholesale water system shall also notify the commission. The commission in the exercise of its general and specific powers to ensure the health, safety, and availability of drinking water served by the utilities subject to its jurisdiction, may order further action that is not inconsistent with the standards and regulations of the department to ensure a potable water supply.
2. (2) If the public water system is a retail water system, then the person operating the retail water system shall notify the retail water system’s governing body and the governing body of any local agency whose jurisdiction includes areas supplied with drinking water by the retail water system. If the retail water system is a water company regulated by the California Public Utilities Commission, then the retail water system shall also notify the commission. The commission, in the exercise of its general and specific powers to ensure the health, safety, and availability of drinking water served by the utilities subject to its jurisdiction, may order further action that is not inconsistent with the standards and regulations of the department to ensure a potable water supply.

(c) For purposes of this section, the following terms have the following meanings:

1. (1) “Drinking water source” means an individual groundwater well, an individual surface water intake, or in the case of water purchased from another water system, the water at the service connection.
2. (2) “Local agency” means a city or county, or a city and county.
3. (3) “Notification level” means the concentration level of a contaminant in drinking water delivered for human consumption that the department has determined, based on available scientific information, does not pose a significant health risk but warrants notification pursuant to this section. Notification levels are nonregulatory, health-based advisory levels established by the department for contaminants in drinking water for which maximum contaminant levels have not been established. Notification levels are established as precautionary measures for contaminants that may be considered candidates for establishment of maximum contaminant levels, but have not yet undergone or completed the regulatory standard setting process prescribed for the development of maximum contaminant levels and are not drinking water standards.
4. (4) “Response level” means the concentration of a contaminant in drinking water delivered for human consumption at which the department recommends that additional steps, beyond notification pursuant to this section, be taken to reduce public exposure to the contaminant. Response levels are established in conjunction with notification levels for contaminants that may be considered candidates for establishment of maximum contaminant levels, but have not yet undergone or completed the regulatory standard setting process prescribed for the development of maximum contaminant levels and are not drinking water standards.
5. (5) “Retail water system” means a public water system that supplies water directly to the end user.
6. (6) “Wholesale water system” means a public water system that supplies water to other public water systems for resale.