Water Supply Overview

Cascade’s 2025 Water System Plan (fka the Transmission & Supply Plan) fulfills Cascade’s responsibility to submit a water system plan to the Washington State Department of Health (DOH). In addition, it supplements information on regional supply presented in each Member’s individual water system plan. The 2025 WSP supersedes Cascade’s 2019 Transmission and Supply Plan Extension, which updated the 2012 Transmission and Supply Plan.

Download the 2025 Water System Plan Chapters 1-6
Download the 2025 Water System Plan Exhibits A-J

Download the 2019 Transmission and Supply Plan Extension

Download the 2012 Transmission and Supply Plan

Cascade has wholesale water purchase contracts with Seattle Public Utilities (SPU) and Tacoma Public Utilities (TPU). Cascade anticipates that the current mix of wholesale purchases and member independent supplies will meet all member needs for decades to come.

Cascade’s regional water service area coincides with the individual service areas of its members. Individual Cascade members are Cascade’s source of quality. Each member owns, operates and maintains its own water distribution systems, including water treatment for their independent water sources (five members have their own independent supplies), maintenance of water quality within their reservoirs and distribution systems; and local monitoring of water quality conditions (some monitoring is shared with SPU or other water systems). At this time Cascade’s existing capital facilities for delivery of municipal water supplies consist solely of the Bellevue-Issaquah Pipeline (BIP) which provides transmission of water purchased from SPU to Issaquah and Sammamish Plateau. Cascade has agreements with Bellevue and Sammamish for operating and maintaining the BIP.

Cascade administers regional water conservation services on behalf of its members. The Conservation Program has a goal to reach total cumulative savings of 0.5 million gallons per day (MGD) from 2020 to 2029.