King County, WA Landscaping Rules: Rainwater Harvesting (2026)
Key Facts
- Governing chapter
- K.C.C. 21A.16 Landscaping and Water Use
- Alternative water source def.
- Stored rainwater, K.C.C. § 21A.06.057
- Meter exemption
- Rainwater-fed outlets skip metered-line rule
- Applies to
- New development under K.C.C. 21A.16.030 only
- Not covered
- Seattle and other cities have own codes
Summary
Unincorporated King County's landscaping code treats stored rainwater as an approved 'alternative water source' for required irrigation and exempts rainwater-fed outlets from the meter-placement rule that applies to municipal-supplied irrigation systems.
All irrigation water outlets, except those using alternative water sources, shall be downstream of the meter used to measure irrigation water use.
D. Irrigation systems shall be subject to the following additional provisions:
1. Systems shall not be located on any:
a. turfgrass slopes exceeding a slope of three horizontal feet to one vertical foot (3:1); and
b. turfgrass portions of median strips.
2. Systems in landscape strips less than five feet in width shall be designed to ensure that overspray and/or runoff does not occur by use of system design options such as low volume emitters.
3. Systems shall be designed to be consistent with the requirements of the hydrozone in which they are located.
4. Systems shall be designed with the minimum average irrigation efficiency of 0.625.
5. The use of automatic shutoff or override capabilities using rain shutoffs or moisture sensors is encouraged.
6. Systems shall utilize a central control valve connected to an automatic controller.
7. Systems shall make provisions for winterization either by providing:
a. manual drains (automatic drain valves are not permitted at all low points), or
b. means to blow out lines with pressurized air.
8. Separate valves shall be used to irrigate plants with differing water needs.
Full Breakdown
K.C.C. 21A.16.330.C, part of the county's Landscaping and Water Use chapter, says all irrigation water outlets "except those using alternative water sources" must sit downstream of the irrigation meter. K.C.C. 21A.06.057 defines an alternative water source as stored rainwater or treated or recycled water suitable for landscape irrigation, and states it is not considered potable. A required landscape irrigation system fed by a rain barrel or cistern therefore doesn't need to run through the metered line other systems do. Chapter 21A.16 applies to new development listed in K.C.C. 21A.16.030, mainly commercial, multifamily and parking-lot landscaping, not typical single-family yards, and only in unincorporated King County.
Violations & Fines
Landscaping installed without the required design or irrigation standards is a Title 21A violation enforced under King County Code Title 23, Code Compliance, per K.C.C. 21A.50.020 and 21A.50.030, not a rainwater-harvesting-specific penalty.
Frequently Asked Questions
Does King County require rainwater harvesting for landscaping?
Does this rule cover Seattle or Bellevue?
Sources & Official References
Other rules in King County
Compare King County to another location·View the Washington landscaping rules overview
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