The Municipal Water Law

Growing communities, agriculture, industry, and the importance of conserving water for fish place increasing demands on our state's water resources. To help meet these growing needs, the state legislature passed the Municipal Water Supply-Efficiency Requirements Act (PDF), commonly called MWL. The MWL was challenged and later upheld by the Washington State Supreme Court. Visit the MWL Legal Challenges page for more information about the lawsuit.

Municipal water suppliers are all Group A community water systems with 15 or more residential connections and Group A non-community systems that provide water for residential uses (such as bathing, cooking, and cleaning) to a non-residential population for 25 or more people for 60 or more days a year.

We believe the law:

Provides more certainty and flexibility for water rights held by water systems.
More closely ties water system planning and engineering approvals by us to water rights administered by the state Department of Ecology.
Improves the ability to plan for future growth.
Offers greater flexibility to solve public health problems with water right changes and transfers.
Advances water use efficiency.
Assures greater reliability of safe drinking water for communities.

We implement the MWL through the following.

Water Use Efficiency. On January 22, 2007, the Water Use Efficiency rule became effective to help conserve water for both the environment and future generations by requiring municipal water suppliers to use water more efficiently.
On February 14, 2008, our Planning and Engineering Rules 331-010 (PDF) were incorporated into WAC 246-290.
Coordination with the Department of Ecology. ECY-DOH Memorandum of Understanding Cover Letter (PDF).
In August 2024, in conjunction with the Department of Ecology, we updated procedures for coordinating water resource issues related to public water systems that involve both agencies. We and the Department of Ecology also developed a Memorandum of Understanding (PDF) and Joint Review Procedures for Planning and Engineering Documents (PDF).
The Department of Ecology developed the Water Resources Program Policy 20230: Municipal Water Law Interpretive and Policy Statement (POL-2030) that explains how they implement the MWL.

Municipal water suppliers now have more water right flexibility and certainty, but they also need to include more information in their water system plan or small water system management program.

The guidance documents and fact sheets below help municipal water suppliers understand the benefits of MWL and comply with these additional requirements for their planning documents.

Documentation that your plan is consistent with local government plans (WAC 246-290-108). This is required for water system plans only, unless you request to expand your water right place of use through your small water system management program. See Local Government Consistency Determination Form (Word).
Identified retail service area (WAC 246-290-100(4)(a)(iv)). This is required for water system plans only. The retail service area is where municipal water suppliers have a duty to serve. See Municipal Water Law—Duty to Provide Service Requirement 331-366 (PDF).
Completed Water Use Efficiency Program (WAC 246-290-810). This is required for water system plans and small water system management programs. For additional information see our WUE Guidebook 331-375 (PDF).
Additional information may be required depending on the situation. Contact your ODW regional planner (see below) to discuss, before submitting additional material.