Municipal water law

Together with the Washington State Department of Health, we regulate municipal water suppliers. As the state's water rights manager, we oversee municipalities' water rights, how much water they have, and where they can use it. The Department of Health is responsible for ensuring safe and reliable drinking water. They also regulate the planning and engineering components of water systems.

We have a memorandum of understanding that describes each agency’s role and responsibilities for regulating municipal water.

What is municipal water law?

Municipal water law governs public water systems, like utilities, to ensure they supply safe and reliable drinking water to the public in a way that is consistent with broader water law. While most water rights are governed by the “use it or lose it” principle — meaning that a water right holder can lose a water right if it’s not beneficially used for an extended period — municipal water rights are not.

Under municipal water law, municipal water suppliers can retain water rights they are not currently using. This gives municipal suppliers certainty about maintaining their water rights while allowing them flexibility to plan for future growth. With this flexibility, however, comes the requirement to conserve water.

Impacts from court rulings

Like many areas of water law, municipal water law is shaped by court rulings.

Historically, we granted utilities and municipal suppliers water rights based on system capacity (their “pumps and pipes”) rather than beneficial use. A Washington State Supreme Court case in 1998, Ecology v. Theodoratus, threw into question whether these rights were valid because they were not based on beneficial use like most other water rights. In response to this uncertainty, the Legislature passed the Municipal Water Law in 2003 to clearly define municipal water suppliers and help clarify the status of their rights.

Two subsequent state Supreme Court cases, one in 2010 and another in 2015, upheld the constitutionality of the Municipal Water Law. A central issue in the cases was that the Municipal Water Law allows us to recognize municipal rights based on system capacity. The court affirmed this but stipulated that municipal suppliers must show reasonable diligence, or potential, to grow into their full water right.

Under current law, rights under “pumps and pipes” certificates are considered to be in good standing and remain as such. However, if a municipal supplier applies to change their right, we must conduct an analysis to determine how much of the right has been beneficially used or is likely to be beneficially used in the future. This is called a tentative determination of extent and validity, which could have two outcomes:

  • If we find that the right has been used in full or is likely to be needed fully in the future, then we will certificate the entire water right.
  • If we determine that part of the right has not been fully used and the water supplier has not shown reasonable diligence to use it fully in the future, we may reduce the water right accordingly.