Legal Challenges to Municipal Water Law

Supreme Court Decides Fate of Municipal Water Law (PDF) - On October 28, 2010 the Washington State Supreme Court affirmed the constitutionality of the Municipal Water Law. The Court upheld all the sections of the MWL challenged in Lummi Indian Nation v. State, holding that they do not violate the separation of powers, and do not facially violate the right to due process.

We created this page to help water system owners understand the history of the lawsuit and how they are affected by the 2010 Supreme Court ruling.


The Washington State Legislature enacted the Municipal Water Law in 2003 to give municipal water suppliers more certainty and flexibility with their water rights. The law also required municipal suppliers to use water efficiently. Since then, the Departments of Health and Ecology have developed rules and guidance to implement the law.

Several Indian tribes, environmental groups, and citizens, had sued the state, contending that several sections of the Municipal Water Law violate the U.S. and State Constitutions.

On June 11, 2008, King County Superior Court Judge Jim Rogers struck down parts of the law. One of the effects of the ruling invalidated the definitions of "municipal water supplier" and "municipal supply purposes." The ruling also affected a section of the law concerning water rights.

On October 28 2010, the State Supreme Court issued a unanimous decision on the state's Municipal Water Law. The Court ruled in favor of the State of Washington.

The Supreme Court ruling overturned the 2008 King County Superior Court decision that said three sections of the Municipal Water Law were invalid because they violated the state constitution's separation of powers.

What does this mean?

The Court ruled that all of the challenged sections of the Municipal Water Law are valid. In particular, the Court upheld sections of the law that define "municipal water supply suppliers" as public and private water utilities that serve 15 or more residential connections.

  • The court also affirmed that water right certificates based on water system infrastructure, rather than actual water usage, are "rights in good standing." This ruling protects the validity of numerous water right certificates held by water utilities serving homes and businesses throughout Washington.
  • Under the lower court ruling, privately owned utilities were exempted from the benefits and obligations of the Municipal Water Law. The Supreme Court's ruling means these utilities now have more flexibility with their water rights, but they also will be required to do more with water conservation by complying with the state's water use efficiency requirements.
  • Customers of these water systems are likely to be hearing more from their water utilities about water conservation. They may be asked to share in the cost of efficiency measures, such as installing customer service meters.

How are your water rights affected?

If you have questions about how your water rights might be affected by the ruling, contact your nearest Department of Ecology regional office.

Related information

For more information

Planning: Kim Moore, 360-236-3113

Water Use Efficiency: Brian Walsh, 360-236-3102