Cascade Supply Program

The Cascade Supply Program (CSP) provides a resilient water future by building vital new water connections within the Puget Sound region. Cascade Water Alliance supports communities by providing safe, reliable, cost-effective drinking water for generations to come.

Cascade member agencies serve nearly 400,000 residents and a business population of 380,000. The CSP is a regional Program to expand and strengthen the area’s water system.

Cascade currently contracts with Seattle Public Utilities (SPU) for drinking water for its seven member agencies. Cascade’s contract with SPU is a declining block water supply agreement. This means that instead of getting a fixed amount of water through the end of the contract, Cascade will get less water over time. Starting in 2040, the amount of water Cascade receives from Seattle will decrease.

In March 2025, Cascade and Tacoma Water finalized two new water supply contracts for Tacoma to begin supplying water to Cascade in 2041. These agreements with Tacoma will allow the region to benefit from existing available water supplies while delaying the development of Cascade’s future water source, the White River–Lake Tapps Reservoir. Delaying the development of the reservoir will reduce overall costs. Cascade plans to use the reservoir for drinking water starting in the 2060s.

The three phases of the Program support a more reliable regional water network in the most cost-effective way possible. This long-term investment strengthens the region, supporting water resiliency, flexibility, and future supply options.

By connecting existing water systems, the CSP creates a more flexible and resilient regional water network. The Program  

• Leverages partnerships and regional collaboration.  

• Lessens the impact on the water environment by using existing capacity of regional partners before developing new sources.  

• Sequences planning and construction to cost-effectively meet future water supply demands. 

• Provides effective long-term planning and predictable costs.  

• Creates opportunities for regional coordination, emergency response, and future connections.  

• Enhances seismic resiliency to supply water during emergencies.  

• Diversifies water resources, expanding access from two to four watersheds.  

• Creates a more redundant and robust system ready for future challenges.   

Questions? Contact the CSP team at CSP@cascadewater.org.