California Code, Government Code - GOV § 66338

(a) For purposes of providing service for water, sewer, or power, including a connection fee, a junior accessory dwelling unit shall not be considered a separate or new dwelling unit.

(b) This section shall not be construed to prohibit a local agency from adopting an ordinance or regulation related to a service or a connection fee for water, sewer, or power, that applies to a single-family residence that contains a junior accessory dwelling unit, so long as that ordinance or regulation applies uniformly to all single-family residences regardless of whether the single-family residence includes a junior accessory dwelling unit.