Cal. Water Code § 10608.20
(a)
(b) An urban retail water supplier shall adopt one of the following methods for determining its urban water use target pursuant to subdivision (a):
(2) The per capita daily water use that is estimated using the sum of the following performance standards:
(4) A method that shall be identified and developed by the department, through a public process, and reported to the Legislature no later than December 31, 2010. The method developed by the department shall identify per capita targets that cumulatively result in a statewide 20-percent reduction in urban daily per capita water use by December 31, 2020. In developing urban daily per capita water use targets, the department shall do all of the following:
(h)
(1) The department, through a public process and in consultation with the California Urban Water Conservation Council, shall develop technical methodologies and criteria for the consistent implementation of this part, including, but not limited to, both of the following:
(i)
(j)