The Municipal Water Law

Growing communities, agriculture, industry, and the need to conserve water for fish are 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.

Summary of 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 (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.

How We Implement the MWL

On January 22, 2007, the Water Use Efficiency rule became effective. It helps conserve water for both the environment and future generations by requiring Water Use Efficiency from municipal water suppliers.

In August 2024, in agreement with Ecology we updated procedures for coordinating water resource issues related to public water systems that involve both agencies.

Together, we developed a Memorandum of Understanding (PDF) to coordinate and guide both agencies’ responsibilities. The agreement includes planning, engineering, and public health and safety matters relating to water systems and resources.

On February 14, 2008, our Planning and Engineering Rules 331-010 (PDF) were incorporated into WAC 246-290. We then developed the Joint Review Procedures for Planning and Engineering Documents (PDF).
We also coordinated with Ecology to divide the responsibilities. Read Cover Letter (PDF).
Ecology developed their own Water Resources Program Policy 20230: Municipal Water Law Interpretive and Policy Statement (POL-2030), which 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.