California Code, Health and Safety Code - HSC § 17921.11

(a) For purposes of this section, “water reuse system” includes both of the following:

(b) The department shall, commencing with the next triennial edition of the California Building Standards Code (Title 24 of the California Code of Regulations), research, develop, and propose building standards, including voluntary Tier 1 or Tier 2 standards of the California Green Building Standards Code (Part 11 of Title 24 of the California Code of Regulations), to reduce potable water use in new residential buildings, including consideration of requiring installation of water reuse systems and consideration of requiring preplumbing of buildings to allow future use of recycled water, onsite treated graywater, or other alternative water sources. In developing these standards, the department shall consider potential impacts on affordable housing, may limit requirements to hotel and motel, multifamily, and market-rate housing, and may limit or exempt the application of standards based on building size, development size, availability or planned availability of recycled water, or as otherwise determined appropriate.