Short definition

In WA, greywater can be used for subsurface landscape irrigation only — drip lines under mulch, or mulch basins around trees. Surface irrigation, toilet flushing, vehicle washing, and lawn-spray application are not covered by the current WA rule. Other states permit broader uses; do not cross-apply California or Arizona rules to a WA system.

What it is

The end uses for greywater vary by state. WA’s rule (Chapter 246-274 WAC) is among the more restrictive, limiting permitted use to subsurface irrigation that doesn’t contact edible plant portions or come into surface contact with humans or pets.

WA-permitted end uses:

  • Subsurface drip irrigation under mulch in landscape beds.
  • Mulch basin (gravel plus plant) for fruit trees, where greywater discharges below grade and never contacts the edible part of the plant.
  • Subsurface irrigation of ornamental landscape.

WA-prohibited end uses:

  • Drinking — greywater is Category 5 (highest hazard).
  • Food preparation, dishwashing, bathing.
  • Surface irrigation — sprinkler, hand-watering exposed soil, lawn-spray application.
  • Pool or hot-tub filling.
  • Vehicle washing — not explicitly addressed in current WA rule, but prohibited as a surface application.
  • Toilet flushing — not covered by the current WA rule (would require additional approval).

Permitted in some other states (NOT WA): toilet flushing, floor washing, vehicle washing, surface lawn application. These appear in California, Arizona, and other state codes — but do not apply to WA installations.

For greywater on edible plants: allowed if the discharge is subsurface and never contacts the edible portion. A mulch basin around a fruit tree, where the greywater goes into the soil below the mulch and is taken up by roots, is permitted. Spraying greywater directly on tomato fruit is not.

Why it matters to a homeowner

The end-use restriction is the most commonly misunderstood part of WA’s greywater rule. Homeowners read California permaculture articles about greywater toilet-flushing and assume it’s available everywhere; it isn’t. Designing a system around an unpermitted end use is a code violation that surfaces at inspection or sale.

The practical consequence: WA greywater is most useful for drip irrigation under mulch in landscape beds and orchards. That single application — laundry-to-landscape via subsurface drip — covers most realistic residential greywater scenarios.

When a contractor or designer proposes a greywater end use, ask: “Where in WAC 246-274 is this permitted?” If they can’t cite the rule for the specific use, push back. WA’s rule is uniform statewide; no county is more permissive than the state rule.

Common variants

  • WA end uses (subsurface only) vs. broader US end uses (varies by state).
  • Greywater on edible vs. non-edible plants — both allowed if subsurface and never contacting edible portion.
  • Light greywater (showers, lavatories, laundry) vs. dark greywater (kitchen — Tier 3 with treatment).

Washington note

The current state of WA greywater end uses, by application:

  • Landscape subsurface drip: allowed (Tier 1 single-family at ≤60 gpd, or Tier 2/3 with design submittal).
  • Mulch basin around fruit tree: allowed if subsurface, no edible-part contact.
  • Drought-summer landscape supplement: allowed (subsurface drip).
  • Toilet flushing: not covered by current rule; would require additional approval.
  • Vehicle washing: not covered; prohibited as surface application.
  • Lawn sprinkler / surface application: prohibited.
  • Pool / hot tub: prohibited (Cat 5).
  • Drinking, food prep, bathing: prohibited (Cat 5).

For a typical WA scenario: a Mason County rural homestead diverts the washing machine to a mulch basin in the orchard. The discharge is subsurface, the fruit-tree roots take up the water, and the system has a three-way diverter to switch back to septic when needed. That setup is WA-compliant under Tier 1.

A Drought-summer Eastside homeowner might consider diverting shower water to a subsurface drip line in landscape beds — also WA-compliant if designed as Tier 1 and permitted with the county.

A Seattle homeowner reading California articles about flushing toilets with greywater needs to recognize that WA doesn’t cover this end use — sticking to subsurface irrigation is the WA-compliant path.