California Code, Health and Safety Code - HSC § 116460

(a) A person shall not operate a public water system without an emergency notification plan that has been submitted to and approved by the department. The emergency notification plan shall provide for immediate notice to the customers of the public water system of any significant rise in the bacterial count of water or other failure to comply with any primary drinking water standard that represents an imminent danger to the health of the water users.

(b) When updating an emergency notification plan pursuant to this section, a public water system may, and is encouraged to, provide notification to water users, by means of other communications technology, including, but not limited to, text messages, email, or social media.

(c) A permit, variance, or exemption may not be issued or amended pursuant to this chapter until an emergency notification plan has been approved by the department.

(d) The department shall adopt regulations to implement this section. The regulations may provide for the exclusion of public water systems from the requirements of this section when, in the judgment of the department, the exclusion will best serve the public interest.