California Green Building Code (CALGreen) – Dual plumbing

To promote the usage of recycled water which helps to reduce down the demand for the portable water requirement.

CALGreen Code Section A5.303.5: Dual plumbing.

New buildings and facilities shall be dual plumbed for potable and recycled water systems for toilet flushing when recycled water is available, as determined by the enforcement authority.


The intent of this measure is to reduce indoor potable water use when recycled water is available in the community. Section 5.303.2 of this code mandates reduced flow rates for indoor potable water use through a prescriptive approach. If a tier is adopted by your city or county, a 12- or 20- percent reduction will likely be required, and there may be a local ordinance in place otherwise for a reduction in water usage. Chapter 15 of the California Plumbing Code regulates the installation of dual plumbing systems for potable and recycled water.

Compliance Method:

Comply with the California Plumbing Code requirements for the use of dual plumbed water systems.


Plan intake: The plan reviewer should confirm on the construction documents that the dual plumbing standards in the California Plumbing Code, Chapter 15, are used in the design.

On-site enforcement: The inspector should verify that dual piping is installed and labeled as specified and in accordance with the California Plumbing Code. If recycled water is immediately intended for use in the project, and not just pre-plumbed, the inspector should witness any testing of the system as required by the California Plumbing Code and collect the results of any tests.

(Excerpted from ‘Guide to the 2022 California Green Building Standards Code Nonresidential’ – Chapter 5)

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