Cal. Health & Saf. Code § 116790
Any water softening appliance in place at a residential dwelling prior to January 1, 1980, in those areas being served by sewage treatment facilities that have been limited with regard to salt loading pursuant to Division 7 (commencing with Section 13000) of the Water Code and for which the appropriate regional water quality control board makes a finding, after adoption of waste discharge requirements and subject to a public hearing, that the control of residential salinity input is necessary to provide compliance with those limitations, may be continued in operation for a period no longer than four years after the regional water quality control board has made its findings. After the four-year period has elapsed, any water softening appliance at that site shall be set at a salt efficiency rating of no less than 2850 grains of hardness removed per pound of salt used in regeneration when regeneration is initiated with clock controls or manually-initiated controls, or shall have regenerations initiated with demand devices. Also, after the four-year period has elapsed, those water-saving devices in shower heads, on faucets, and in toilet reservoirs, as recited in paragraph (2) of subdivision (b) of Section 116785, shall be installed unless already in place or prohibited by local and state plumbing and building standards. The salt efficiency rating of the water softening or conditioning appliance and the installation of water-saving devices shall be certified in accordance with Section 116795.
Ca. Health and Saf. Code § 116790