Greywater

Short definition

Greywater is wastewater from showers, sinks, and washing machines (light greywater) or from kitchen sinks and dishwashers (dark greywater). Reusing it for landscape irrigation can substantially cut potable water use. In WA, Chapter 246-274 WAC permits subsurface irrigation only, under three tiers based on flow and source. Surface application is prohibited.

What it is

Greywater is everyday household wastewater that doesn’t include toilet waste (that’s blackwater, which is never reused). It’s “grey” because it carries some contamination — soap, hair, food particles, fabric lint, body oils — but at much lower risk than blackwater.

WA’s framework uses three tiers:

• Tier 1 — single-family residence; ≤60 gallons per day total flow; light greywater only (lavatories, showers, washing machines for domestic laundry); served by approved sewer or on-site septic. The DIY-scale tier most homeowners care about.
• Tier 2 — light greywater serving residential or non-residential building; connected to approved sewer or large on-site septic; design submittal required.
• Tier 3 — light or dark greywater (kitchen sink, dishwasher) serving residential or non-residential; treatment component required; design submittal.

WA-permitted end use is subsurface irrigation only — drip irrigation under mulch, mulch basins around fruit trees. Surface application (spraying, hand-watering exposed surfaces, lawn sprinkler) is prohibited. This differs from California and Arizona rules; do not cross-apply.

System components for a Tier 1 setup:

1. Three-way diverter valve at the source — lets you switch between greywater reuse and the sewer or septic.
2. Filtration — debris removal at the system inlet.
3. Surge tank — short-term flow buffering, typically less than 24 hours of storage; long-term storage isn’t allowed.
4. Subsurface distribution — drip lines under mulch, or mulch basins.
5. Diverter to sewer/septic always available — required by code for system failure response.

Backflow protection: greywater is Category 5 (highest hazard) for cross-connection control purposes. Air gap or RPZ separation from the potable system is mandatory.

Why it matters to a homeowner

For a permaculture-oriented homeowner or a rural property with limited water capacity, greywater is one of the highest-leverage water-conservation systems. A typical washing machine produces 15–40 gallons per cycle; routing that to subsurface drip in fruit trees or landscape can save thousands of gallons over a summer.

For most urban WA homeowners, the calculus is different. The complexity of a code-compliant system, the cross-connection backflow requirements, and the seasonal limits (frozen lines in Eastern WA, low summer flow in dry years) often make rainwater harvesting a more practical first move. A laundry-to-landscape Tier 1 install is feasible DIY for an experienced homeowner, but requires careful attention to the WA subsurface-only rule.

When a designer or contractor proposes a greywater system, three questions to ask: (1) Which tier is this and what permit applies? (2) Where is the diverter so I can switch off the system at any time? (3) What’s the system failure response — how does greywater get diverted to sewer or septic if the system fails or freezes?

Common failure modes

• Filter not maintained — clogs distribution.
• Improper biological or chemical conditions — odor.
• Frozen lines (Eastern WA) — no winter operation; switch to sewer divert.
• Cross-connection to potable — catastrophic Cat 5 hazard; air gap or RPZ mandatory.
• Improperly sized to peak flow — overflow or surface ponding (also a code violation).
• Surface application in WA — code violation; immediately divert.

Common variants

• Light greywater (showers, lavatories, laundry) vs. dark greywater (kitchen, dishwasher — Tier 3 with treatment).
• Greywater (reusable) vs. blackwater (toilet, never reused).
• Subsurface irrigation (only WA-allowed end use) vs. surface irrigation (prohibited in WA).
• Direct reuse (no storage) vs. treated and stored (Tier 3).
• Tier 1 (DIY-scale, simpler) vs. Tier 2/3 (engineered, design submittal).

Washington note

WA’s greywater framework is Chapter 246-274 WAC, effective July 31, 2011, and administered by the Department of Health (DOH) Greywater Reuse program in coordination with county health departments.

Tier selection depends on flow and water source:
– Tier 1: ≤60 gpd, single-family, light greywater only.
– Tier 2: larger, light greywater, design submittal.
– Tier 3: dark greywater plus treatment, design submittal.

Failure response is required by rule: if a Tier 1/2/3 system fails or is suspected to fail, the owner must immediately divert greywater to approved sewer or on-site septic. The three-way diverter valve is the mechanism for this and is effectively code-required for any compliant WA system.

Permitted end uses (per current WAC): subsurface irrigation only. Toilet flushing, vehicle washing, surface irrigation, and lawn-spray application are not covered by the current WA rule. Some other states permit those uses; do not cross-apply.

County-specific permitting: counties (King, Pierce, Snohomish, Thurston, Mason, Jefferson, Kitsap, Spokane) issue specific permits and may add local rules. Verify per-county before installing. Some counties allow self-certification for Tier 1; others require a designer signature.

Backflow protection: greywater is Category 5 (highest hazard). Air gap or RPZ separation from the potable supply is required by cross-connection control rules.

For a rural Mason County or Olympic Peninsula homestead, a Tier 1 greywater system can pair well with rainwater harvesting and a composting toilet to dramatically reduce potable water demand. Verify the county’s specific permitting workflow before designing.

FAQ

Can I send my greywater to the lawn sprinkler?

No. WA permits subsurface irrigation only — drip under mulch or mulch basins. Surface application (sprinklers, hand-watering exposed soil) is prohibited under WAC 246-274.

Can I use greywater to flush my toilet in WA?

The current WA rule covers subsurface irrigation only. Toilet-flushing greywater systems are not covered by WAC 246-274 as written and would require additional approval. Some other states permit this; WA does not under the current rule.

Do I need a permit for a Tier 1 system?

Yes. Even Tier 1 (≤60 gpd single-family) follows the WA rule. The “regulatory exemption” misconception is common but wrong — the state rule applies. Some counties allow self-certification for Tier 1; others require a designer. Contact your county health department.