About On-site Nonpotable Water System (ONWS)
- An on-site nonpotable water system (ONWS) is 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 include “nonpotable reuse systems” under Chapter 173-219 WAC "alternate water source systems” under WAC 51-56-1500 and “nonpotable rainwater catchment systems” under WAC 51-56-1600.
- All existing ONWS are required to obtain a permit.
- We used guidance from the National Blue-Ribbon Commission to develop the ONWS rule Please see the Water Reuse Association for more information.
Projected Impacts
- Reduce the amount of pollutants entering waterways and improve water quality.
- Reduce the demand on 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 by capturing and treating stormwater and putting it to 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.
Sources of Water
Allowable source waters include:
- Greywater: wastewater from bathroom sinks, showers, bathtubs, clothes washers, and laundry sinks
- Blackwater: wastewater from toilets, urinals, kitchen sinks, and dishwashers
- Stormwater
- Rooftop runoff
- Foundation drainage
- Air conditioning condensate
Beneficial End Uses
- Toilet and urinal flushing
- Priming drain traps
- Clothes washing
- Subsurface irrigation, surface nonspray irrigation, and spray irrigation of nonfood plants
- Dust control and street cleaning
- Other end uses approved under the variance procedure described in (1) WAC 246-945-145
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 from WAC 246-275-300 to WAC 246-275-330 for specific ONWS design requirements.
ONWS Installer
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 from WAC 246-275-400 to WAC 246-275-525 for more details on certification(s) and duties.
Department Fees
During ONWS review, the department shall collect the following non-refundable fees:
| Category | Base Fee | Hourly Fee |
| Initial Design Review Minor Project | $1548 for four hours | Additional time to be billed at hourly rate |
| Initial Design Review Major Project | $3096 for eight hours | Additional time to be billed at hourly rate |
| Hourly rate for engineer review | N/A | $387 |
| Annual operating permit review | $2572 | N/A |
| Permit review late fee | $466 | When submitted after due date |
| Expired permit fee | $1280 | When submitted after due date and includes late fee and re-permitting |
Contact Us
Email the Wastewater Management Section or call 360-236-3330.