California Code, Water Code - WAT § 390

(a) “Costs of water service for the highest users” means the difference in costs, including applicable capital costs and operation and maintenance costs, that the public entity incurs directly, or by contract, as a result of the increased water service required by its high water users.  “Costs of water service for the highest users” may be reported by customer class, rate classification, or cumulatively, and may include any of the following:

(b) “High water users” means the top 10 percent of water, in terms of volume of water consumed.  Alternatively, for a public entity that has allocation-based conservation water pricing pursuant to Section 372, the public entity may define high water users as those customers whose water use is above the water budget assigned to them by that public entity.

(c) “Public entity” means a city, whether general law or chartered, county, city and county, special district, agency, authority, any other municipal public corporation or district, or any other political subdivision of the state that provides retail water service and that is an urban water supplier, as defined in Section 10617.

(d) “Water usage demand analysis” means an analysis conducted to determine water usage patterns and demands placed on a water system operated by a public entity.