On-site Nonpotable Water Systems

About On-site Nonpotable Water System (ONWS)

• Definition of ONWS: “On-site nonpotable water system (ONWS)” means a system in which water from local sources is collected, treated, and used for non-potable uses at the building to district/neighborhood-scale, generally at a location near the point of generation. ONWS includes “nonpotable reuse system” under chapter 173-219 WAC, “alternate water source system” under WAC 51-56-1500, and “nonpotable rainwater catchment system” under WAC 51-56-1600.  
• All existing are required to obtain a permit by [timeline] (get from WAC)
• The National Blue-Ribbon Commission is the ruling criteria we followed. Please click on the following to learn more: WateReuse Association

 ONWS’ Projected Impacts

• Reduce the amount of pollutants entering waterways and improve water quality.
• Reduce the demand for sewage treatment plants and the amount of sewage treatment plant effluent emptied into rivers and the ocean.
• Reduce water consumption by providing an alternative source of water for non-potable uses.  
• Bolster local water supplies.
• Increase resilience to drought by providing a backup source of water in times of scarcity.
• Manage polluted stormwater runoff and flooding by capturing and treating rooftop runoff and stormwater and putting it to beneficial use.
• Save energy by reducing the need to treat and distribute potable water. 
• Reduce the need to pump imported water over long distances. 
• Protect water resources by reducing the need to remove fresh water from natural habitats. 
• Refer to ruling link for more details

Sources of Water

Allowable source waters include:

• Greywater, which is water from bathroom sinks, showers, bathtubs, clothes washers, and laundry sinks.
• Blackwater, which is wastewater from toilets, urinals, kitchen sinks, and dishwashers
• Stormwater
• Rooftop runoff
• Foundation drainage.
• Air conditioning condensate.

Nonpotable source waters are valuable natural resources.  This water can now be collected, treated on-site or nearby and put to beneficial use—where high-quality drinking water, or potable water, is not needed. 

Beneficial End Uses

(a) Toilet and urinal flushing.

(b) Priming drain traps.

(c) Clothes washing.

(d) Subsurface irrigation, surface nonspray irrigation, and spray irrigation of nonfood plants.

(e) Dust control and street cleaning.

(f) End uses approved under the variance procedure described in WAC 246-275-145(1).

Implementation Scale

• Multifamily residential.
• Commercial.
• Mixed-use buildings.
• District-scale projects, which can include a mix of the above.

ONWS Purveyor

The ONWS purveyor is responsible for operating the ONWS and meeting rule requirements and permit conditions.

ONWS Designer

A professional engineer, licensed in the State of Washington, must prepare and stamp all ONWS design documents and reports submitted to the Department of Health (Department) for review and approval. 

Please look at WAC 246-275-300-330 for specific ONWS design requirements.

ONWS Installers

The ONWS installer must be a licensed contractor by the state of Washington (RCW 18.27.010). A licensed plumber needs to install all distribution piping/fixtures/appliances/appurtenances inside a commercial or multifamily (Chapter 18.27 RCW, Plumber Certification).

ONWS Operator

An operator’s role is to manage daily and ongoing maintenance and operations of ONWS. The operator must have expertise, commensurate with the complexity of the operation and maintenance of the ONWS and hold a valid department-issued certification as a cross-connection control specialist. Please look at WAC 410 for more details on certification(s) and duties.

Please look at WAC 246-275-400 -525 for details.

Department Fees

During ONWS review, the department shall collect the following non-refundable fees: 

Contact Us

Email the Wastewater Management Section or call 360-236-3330.