Summary of Washington’s Water Reuse Guideline or Regulation for Landscaping and Onsite Non-potable Water Reuse
This page is part of the EPA’s REUSExplorer tool, which summarizes the different state level regulations or guidelines for water reuse for a variety of sources and end-uses.
The source water for this summary is Rainwater Collected Onsite.
- Technical basis
- Onsite non-potable reuse approved for use in Washington
- Water reuse category/type
- Additional context and definitions
- Onsite non-potable reuse specifications (table)
- Upcoming state law or policy
- References
- Disclaimer
This page is a summary of the state’s water reuse law or policy and is provided for informational purposes only. Please always refer to the state for the most accurate and updated information.
In Washington, water reuse for landscapingThe use of recycled water on land to assist in the irrigation of vegetation in residential and non-residential areas. Includes impoundments to store water for irrigation , ornamental vegetation, parks, school yards, sporting facilities (including golf courses), private gardens, roadsides and greenbelts, and cemeteries. Excludes irrigation of areas used for agriculture, commercial reuse applications, or any centralized non-potable reuse. reuse applications include aboveground irrigation and subsurface or drip irrigation, and onsite non-potable water reuse The use of treated onsite collected waters for non-potable purposes at the single-building or district scale. This reuse application excludes the use of recycled water from a centralized treatment and distribution system for landscape irrigation or commercial uses. applications include water closets, urinals, tap primers, car washing, cooling tower makeup and water features. The source of water rainwater collected onsite Precipitation collected at the district or regional scale is classified separately under 'stormwater.' is specified by the state as harvested rainwater. The write-up uses state terms when discussing sources or uses of water that may differ from the Regulations and End-Use Specifications Explorer's (REUSExplorer's) terms.
Check out Washington's other landscaping summary!
State requirements for water quality and treatment are often associated with the source water. Washington has a landscaping summary page where the source water is treated municipal wastewater.
Technical basis
Washington approves the use of rooftop collected rainwater for onsite non-potable water reuse applications, including irrigation, water closets and urinals, primers for floor drains and sinks ornamental fountains and water features, cooling tower water and car washing (Wash. Rev. Code § 90.03; Wash. Rev. Code § 90.54). All applicable provisions of the Clean Water Act (CWA) (33 U.S.C. §§ 1251 et seq.), including its implementing regulations, must be met in addition to any state water quality standards. A water right permit is not required for rooftop collected rainwater for non-potable onsite water reuse applications given that the rainwater collected exterior of a building (WPC, 2021) is reused on the same property that the water was collected and can only be collected from existing structures with purposes other than collecting rainwater (Wash. Rev. Code § 90.03; Wash. Rev. Code § 90.54). In all other cases, Washington requires a water right permit for installation or alteration of a rainwater catchment system. Treatment requirements and performance standards are applied for the removal of microbial contaminants and other relevant indicators related to onsite non-potable water reuse and are summarized in the table. The technical basis for developing the specifications and/or removal of microbial contaminants and other relevant indicators is not explicitly specified.
Onsite non-potable water reuse applications approved for use in Washington
The Washington Plumbing Code (WPC, 2021) defines the following specific onsite non-potable water reuse applications for rainwater catchment systems:
- Aboveground irrigation
- Subsurface or drip irrigation
- Water closets
- Urinals
- Tap primers for floor drains and floor sinks
- Ornamental fountains and other water features
- Cooling tower makeup
- Car washing
Additional onsite non-potable water reuse applications for treated rainwater are not specified.
Water reuse treatment category/type
Washington does not assign harvested rainwater used for onsite non-potable water reuse to a category or class but specifies that each application of rainwater reuse must meet minimum water quality requirements for the intended use application (WPC, 2021).
Specific treatment requirements are provided for non-potable rainwater catchment systems with the exception of those for subsurface or non-sprinkled surface irrigation where the maximum storage volume is less than 360 gallons (WPC, 2021). Devices and equipment used to treat harvested rainwater must be designed, sized and documented by a Washington State registered professional engineer (WPC, 2021). Briefly, treatment requirements include:
- Filtration: All onsite non-potable water systems, including rainwater catchment systems, must include filtration mechanisms for rainwater in the form of a debris excluder or other approved means to prevent accumulation of leaves, needles, sediment and other debris from entering the storage tank (WPC, 2021). Debris should be inspected and cleared every 6 months and tree branches and vegetation overhanging catchment systems should be removed as needed (WPC, 2021). Devices used to remove debris or sediment must be accessible and installed in accordance with manufacturer instructions (WPC, 2021). Collected rainwater must be further filtered as required for the intended end use (WPC, 2021). Specifically, non-potable water utilized for water closets, urinals, tap primers and drip irrigation must be filtered by a 100-micron filter (WPC, 2021). Filters should be inspected, cleaned and replaced every 3 months (WPC, 2021).
- Disinfection: Harvested rainwater must be disinfected by an acceptable method, including chlorination, ultraviolet sterilization, ozone or similar means as necessary to meet water quality requirements specific for the intended onsite water reuse application (WPC, 2021). Disinfection devices must be approved for the intended application that are third-party certified (WPC, 2021). Water quality should be tested every 12 months and following system renovation or repair (WPC, 2021).
Additional context and definitions
In Washington, all rainwater collected for non-potable reuse must be collected from roof surfaces or other man-made, above-ground collection surfaces (WPC, 2021). All rainwater catchment systems must be installed by a Washington State certified plumber in accordance with the Washington State Plumbing Code (WPC, 2021) (Wash. Rev. Code § 51-56). Collecting precipitation from rooftops must comply with standards defined by the American Society of Plumbing Engineers and American Rainwater Catchment Systems Association (ARCSA/ASPE/ANSI 63-2020). Precipitation collected from other surfaces (e.g., surface water runoff, vehicular parking surfaces or man-made surfaces at or below grade) must be in accordance with stormwater requirements for on-site treated non-potable water systems (WPC, 2021).
Washington requires all maintenance, testing and inspection of non-potable rainwater catchment systems to be recorded in the form of a maintenance log by the property owner and available for inspection (WPC, 2021). Following the construction of a rainwater catchment system, an operation and maintenance manual is required. The manual must include a detailed diagram of the entire system, instructions for operating and maintaining the system, details on maintaining required water quality, details on deactivating the system, applicable testing, inspection and maintenance frequencies and manufacturer contact information (WPC, 2021).
Washington outlines specific requirements for collection, distribution and drainage materials for non-potable rainwater catchment systems. Rainwater catchment systems must be constructed of materials compatible with the water treatment and conditions in the system (WPC, 2021). Water supply and distribution materials utilized in rainwater catchment systems must be constructed of like materials and comply with requirements for potable water supply and distributions defined by the WPC (2021). Rainwater catchment system drainage materials including gutters, downspouts and leaders must comply with storm drainage requirements outlined by the WPC (2021).
Non-potable rainwater catchment systems must be compatible with the pipe and fitting materials, water treatment and water conditions (WPC, 2021). Rainwater storage tanks must be constructed of solid, durable, water-tight materials not subject to excessive corrosion or decay (WPC, 2021). Washington allows both above and below grade non-potable water storage tanks, under the requirements summarized in the WPC (2021).
All components of the storage tanks must be designed with proper means of access, draining and cleaning. The storage tanks openings must have protection against entrance of animals into the tank. The opening of the storage tank must exceed 12 inches (305mm) in diameter and secured to prevent tampering and unintended entry by a lockable device or other approved method (WPC, 2021). Rainwater storage tanks must be designed for drainage and overflow, where the overflow drain is not equipped with a shutoff valve (WPC, 2021). The outlet for overflow must discharge in accordance with the WPC (2021) for storm drainage system requirements, with protection from backflow by a backwater valve or other approved method. Where venting using drainage or overflow piping is not provided or is insufficient, a vent is required to be installed on the storage tank (WPC, 2021).
All non-potable rainwater storage tanks must be made identifiable with the words “NONPOTABLE RAINWATER” permanently marked. Where openings are provided for entry, the opening must be marked with the language “DANGER--CONFINED SPACE” (WPC, 2021). Commercial and institutional restrooms using non-potable rainwater for water closets or urinals require signage made visible to users with the words “TO CONSERVE WATER, THIS BUILDING USES RAINWATER TO FLUSH TOILETS AND URINALS” (WPC, 2021). Equipment rooms containing non-potable rainwater equipment must have a sign posted with the words “CAUTION NONPOTABLE RAINWATER, DO NOT DRINK. DO NOT CONNECT TO DRINKING WATER SYSTEM. NOTICE: CONTACT BUILDING MANAGEMENT BEFORE PERFORMING ANY WORK ON THIS WATER SYSTEM” (WPC, 2021).
Onsite non-potable water reuse specifications
Summary of Washington's Onsite Non-potable Water Reuse Specifications
| Recycled Water Class/Category | Source Water Type | Water Quality Parameter | Specification | Sampling/Monitoring Requirements (Frequency of monitoring; site/ location of sample; quantification methods)* | |
|---|---|---|---|---|---|
| Non-potable water applications including spray irrigation where maximum storage volume is ≥350 gallons; urinal and water closet flushing; clothes washing; tap priming; ornamental fountains and other water features; cooling tower make-up watera | Rainwater | E. coli | <100 CFU/100mL | Water quality must be tested every 12 months and following system renovation or repair. | |
| Turbidity | <10 NTU | ||||
Source = WPC (2021)
* Information about sampling and monitoring requirements such as frequency, site and quantification methods not specifically listed in the table was not explicitly specified in the State-specific regulations.
a Inspect and verify water quality treatment devices and systems are operational and maintaining minimum water quality requirements in accordance with manufacturer’s instructions.
Upcoming state law or policy
No upcoming onsite non-potable water reuse regulations related to rainwater were found for Washington.
References:
Clean Water Act. 33 U.S.C. §§ 1251 et seq.
On-Site Nonpotable Water Systems—Risk-Based Water Quality Standards, Wash. H.B. 1184 (2021).
State Building Code Adoption and Amendment of the 2021 Edition of the Uniform Plumbing Code. Wash. Rev. Code § 51-56-0100.
State of Washington Department of Ecology (ECY). 2009.
Washington Plumbing Code (WPC). 2021. Chapter 16 Nonpotable Rainwater Catchment Systems.
Water Code. Wash. Rev. Code § 90.03.
Water Resources Act of 1971. Wash. Rev. Code § 90.54.
Please contact us at waterreuse@epa.gov if the information on this page needs updating or if this state is updating or planning to update its laws and policies and we have not included that information on the news page.