Water Treatment Plant General Permit

Water treatment plants produce water for drinking and for industrial businesses. The Washington State Department of Health assures drinking water is safe and reliable. Our role ensures that the water treatment byproducts released from these plants do not harm the environment.

Treatment can involve:

  • Filtering and settling out sediment and disease-causing organisms.
  • Using chemicals to kill organisms or remove excess minerals and other contaminants.
  • Disinfection and chemical adjustment to reduce scaling or corrosion within the delivery system.
We have developed the Water Treatment Plant General Permit (WTPGP) to help treatment facilities comply with state laws and the Federal Water Pollution Control Act. This permit contains specific requirements and conditions for permittees to protect rivers and other waterbodies that receive wastewater discharges.

The current permit went into effect Sept. 1, 2014, and expires on Aug. 31, 2019.

Current permit documents

Water Treatment Plant Reports 

During the past four years, we reviewed recent data concerning water treatment plants in Washington, including:
  • Arsenic monitoring data provided by WTPGP permittees.
  • Data about raw water sources, finished water production rates, volumes of wastewater discharged, and populations served for more than 900 water treatment plants statewide.
The two reports identified below summarize that work and our findings and conclusions.

Permit Reissuance — 2018/2019

The current Water Treatment Plant General Permit expires on August 31, 2019. We plan to re-issue an updated general permit for wastewater discharges from water treatment plants in mid-summer 2019. Our process has several steps where we will be asking for feedback from stakeholders and other interested parties. 

Workshop and listening session

On July 10, 2018, at Ecology Headquarters in Lacey, WA, and via webinar, we presented our plan for the Water Treatment Plant General Permit and solicited suggestions for the new permit from current permit holders and other interested parties. View the workshop presentation slides (pdf).


  • Draft permit public comment period: Spring 2019
  • Issue final permit: Summer 2019
  • Permit effective: Summer/Fall 2019
If you want to be included in future emails concerning the reissuance of the water treatment plant general permit, please email james.maroncelli@ecy.wa.gov.

Does my facility need this permit?

You need this general permit if your water treatment plant discharges wastewater to surface waters and:

  • Produces 35,000 gallons per day or more (monthly total divided by the number of days in the month) of finished drinking and industrial water.
  • The primary function of the facility is treatment and distribution of potable or industrial water.
  • Produces wastewater by filtration processes.
  • Is not a part of a larger permitted facility.

Operations not covered by this permit include discharge of wastewater that is:

  1. Produced by one of the following processes:
    • Ion exchange
    • Reverse osmosis
    • Slow sand filtration
  2. Sent to a publicly-owned treatment works.
  3. Released to land where runoff or overflow is impossible.

If any of these are the case, you may need an individual permit.

How to request coverage under this permit

Request coverage under this permit from the following online resources, or contact the permit administrator in your region.

Previous permit documents

For assistance contact your permit administrator


Marcia Porter
Permit Manager

Eastern Northwest Southwest