No regulation or ordinance of a district which regulates or prescribes standards for the installation of plumbing inside of buildings and structures, shall be effective within any county, city and county, or city which has adopted an ordinance, regulation, or code incorporated in an ordinance governing such installations.
Source:
Section 6522.1, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC§ionNum=6522.1..