What rules apply to a residential graywater system?

Start with the water source and intended use

A laundry-to-landscape diversion, a pumped irrigation system, and a treatment system for
toilet flushing are different projects. Identify the source drains, expected daily volume,
treatment equipment, plumbing changes, and where the water will go before choosing a design.
Permission for one use does not establish permission for another.

State rules and local permits

California: Water Code § 14875
applies the graywater chapter to construction, installation, and alteration of systems for
subsurface irrigation and other safe uses. It is a scope provision, not a complete design
standard or an answer to whether your system needs a permit.

For a concrete local example, Santa Cruz County’s guidance
describes a permit exemption for irrigation systems in one- or two-unit residential
buildings that collect only eligible laundry water, have no pump or tank, and do not alter
the building’s existing plumbing. Water from laundering diapers or other prohibited content
is excluded. The county requires permits for other residential graywater designs. Even an
exempt system must comply with the applicable plumbing requirements. Confirm the current
conditions with your own local authority; the county example is not a nationwide exemption.

Arizona: ARS § 49-204(A)
limits city, town, and county restrictions on graywater use. Its exception combines a
specified initial active-management-area setting, an assured-water-supply determination
that includes effluent, and a reduction in effluent available to meet that determination.
Do not reduce that exception to a general permission for any locality to prohibit reuse.

Subsections (B)–(D) address indoor toilet flushing with treated graywater. They authorize
health and safety rules, specify interim conditions until those rules are adopted, and
require later-installed systems to meet the adopted requirements. The interim text includes
less than 400 gallons per day, specified treatment-system certification, protection from
human contact, dedicated piping, and proper operation. Check the current rule and permit
requirements before relying on that interim pathway.

Colorado: HB24-1362, effective January 1, 2026, authorizes qualifying graywater systems and use, subject to the state rules. A county or municipality may prohibit all graywater or specified categories by ordinance or resolution. Unless local law allows otherwise, indoor systems under this authorization are limited to new construction. Water-right decrees, contracts, well permits, and return-flow conditions remain applicable. Confirm the local opt-out status, plumbing requirements, and water-source conditions before installation.

Assess an HOA restriction separately

A law limiting municipal ordinances does not, by itself, answer whether a private HOA rule
is enforceable. Obtain the proposed restriction and the governing provision the association
relies on, then compare them with the law covering the project.

In California, Civil Code § 4735
limits restrictions on specified water-conserving landscaping and on compliance with listed
water-efficient landscape ordinances and water-use rules. Whether that protects an aspect
of your graywater project depends on the actual ordinance, design, and restriction. It is
not a universal approval for every irrigation system.

In Arizona planned communities, ARS § 33-1817(B)
bars unreasonable withholding of approval of a construction project’s architectural designs,
plans, and amendments. Ask the association to identify the design concern and the basis for
its decision. Shared pipes, common land, and work affecting another owner require their own
property-rights analysis.

What to do next

1. Give the local permit office a description of the source fixtures, flow, treatment,
   intended use, and plumbing changes. Ask which current code provisions apply.
2. Establish whether a permit or exemption applies and retain the authority’s response.
3. Check ownership of the proposed installation area and any affected shared plumbing.
4. For a lawfully required HOA application, include the design and the applicable water
   or landscaping provisions; save the application, receipt, and decision.
5. Have the installer document maintenance, overflow or diversion arrangements, and any
   required inspections. A licensed plumber or engineer can resolve design questions; an
   association-law attorney can assess a disputed private restriction.

Keep the final plans, equipment information, permit or exemption record, inspection results,
and written approval conditions together. Update that record if the source drains, use, or
system design changes.