Cal. HSC § 106885

(a) (1) A person who operates a water treatment plant shall possess a valid, unexpired water treatment operator certificate of appropriate grade in accordance with the regulations adopted pursuant to Section 106910. (2) A person who is in responsible charge of the water treatment plant shall possess a valid, unexpired water treatment operator certificate equal to or greater than the classification of the water treatment plant. (b) (1) A person who operates a water distribution system shall possess a valid, unexpired water distribution operator certificate of the appropriate grade in accordance with the regulations adopted pursuant to Section 106910. (2) A person who is in responsible charge of the water distribution system shall possess a valid, unexpired water distribution operator certificate equal to or greater than the classification of the water distribution system.