Buying Land in Washington: Growth Management, Water Rights, and Septic Rules

The Growth Management Act sets rules most counties' zoning has to follow

Washington's 1990 Growth Management Act (GMA, codified at RCW 36.70A) requires the state's most populous and fastest-growing counties -- along with the cities inside them -- to adopt a comprehensive plan and development regulations that designate Urban Growth Areas (UGAs), protect Critical Areas, and designate Agricultural, Forest, and Mineral Resource Lands for conservation. Roughly 28 of Washington's 39 counties currently fully plan under the GMA, covering most of the state's population; some are required to under the statute's population/growth thresholds, others opted in voluntarily, and a smaller number aren't required to fully plan at all. Which category a given county falls into isn't something to assume -- verify it directly.

In a fully-planning county, zoning isn't purely a local, ad-hoc decision: the comprehensive plan, UGA map, resource-land designations, and critical-areas ordinance all have to comply with the GMA's requirements, and the state Growth Management Hearings Board can hear challenges when a local plan doesn't. The zoning designation on a specific parcel is doing real legal work, not just describing a local preference.

What this means for rural land: UGAs, resource lands, and critical areas

GMA counties must direct urban-density growth inside their UGAs and keep land outside them rural, agricultural, forest, or otherwise resource-designated. That produces real, mapped restrictions outside a UGA: minimum lot sizes for new rural land divisions are often large (commonly several acres to 20+ acres, depending on the county's adopted density), and land designated Agricultural, Forest, or Mineral Resource Land under RCW 36.70A.170 carries added protections aimed at conserving it for that use, which can limit non-resource building rights even when the base zoning nominally allows a dwelling.

Every fully-planning county also designates and protects Critical Areas -- wetlands, geologically hazardous areas, fish and wildlife habitat, frequently flooded areas, and critical aquifer recharge areas -- under a local critical areas ordinance. Buffer widths and allowed uses vary by county and critical-area type, so a parcel that looks buildable on a zoning map can still carry a substantial buffer a zoning letter alone won't show.

• Confirm whether the parcel is inside or outside the county's Urban Growth Area -- that single line determines which set of density and use rules applies.
• If the parcel carries an Agricultural, Forest, or Mineral Resource Land designation, ask the county planning department directly whether -- and under what conditions -- a new dwelling is allowed.
• Ask specifically whether any part of the parcel falls inside a mapped critical area or its buffer before assuming the whole lot is usable.

Water rights: prior appropriation, with real limits on new wells in some basins

Washington is fundamentally a prior-appropriation ('first in time, first in right') state for both surface water and groundwater, administered by the Department of Ecology, though some older riparian-era claims predating the state's water codes still exist layered underneath that system. For most new uses, a water right permit from Ecology is required before water can legally be withdrawn.

The major exception buyers rely on is the permit-exempt well under RCW 90.44.050, allowing limited groundwater withdrawals -- e.g., single or group domestic use up to 5,000 gallons a day, stock watering, or a lawn/garden under a half acre -- without Ecology's full permitting process. It's narrower than many buyers assume, and has gotten more complicated, not less, over the past decade.

In its 2016 Whatcom County v. Hirst decision, the Washington Supreme Court held that counties can't simply rely on the RCW 90.44.050 exemption when deciding whether to permit a home relying on a new well -- counties must independently confirm legally and physically available water exists. The legislature responded in 2018 with ESSB 6091 (largely codified at RCW 90.94, the Streamflow Restoration Act), shifting water-availability determinations to Ecology-adopted watershed restoration plans for specific Water Resource Inventory Areas (WRIAs), and imposing a fee and withdrawal cap on new exempt wells within the WRIAs it covers. Whether a parcel can support a new exempt well -- and on what terms -- depends on its WRIA and that basin's plan, not one statewide rule, and this area keeps changing legislatively, so confirm current status rather than assuming.

Septic (on-site sewage systems): a state minimum standard, permitted locally

If a parcel isn't on a public sewer system, it needs an on-site sewage system, regulated statewide under WAC 246-272A, adopted by the State Board of Health and administered jointly by the Department of Health (DOH) and local health officers. The chapter sets statewide minimum design, siting, and performance standards, but local health jurisdictions -- generally the county health department -- can and do adopt stricter local requirements, and they're the ones who issue permits, review site evaluations, and inspect installations. The technical floor is set once at the state level, but the office you deal with is county-specific -- see our national guides to perc tests and septic systems for how the underlying process works.

What's still decided at the county level

The GMA, the state water code, and WAC 246-272A are real, statewide (or in the water case, basin-specific) frameworks, but the answers that actually determine whether a specific parcel is buildable are still assembled locally: whether the county fully plans under the GMA at all, the exact UGA boundary and rural zoning density that applies to a parcel, whether a resource-land designation blocks a new dwelling, critical-area buffer widths, which WRIA governs a parcel's well options and what that basin's restoration plan requires, and which local health jurisdiction issues the septic permit.

This page tells you what kind of system Washington runs and which agencies to expect -- it does not tell you whether a specific parcel can be divided, built on, or supplied with a legal well. Those answers come from the county planning department, Ecology (for the applicable WRIA), and the local health jurisdiction, every time.