Water Planning | Supply Plan Overview

Transmission & Supply Plan (TSP) Overview

The Cascade Transmission and Supply Plan was adopted in July 2012, fulfilling Cascade’s responsibility to the Washington State Department of Health (DOH). It supplements information on regional supply provided by each of its members in their respective individual water system plans. The plan describes Cascade’s current water supplies and operations and also its plans for development of additional water supplies to meet the needs of Cascade members through 2060. The Cascade TSP was approved by the King County Council in February 2013 and by DOH in March 2013. The next update of the Cascade TSP is due in 2019.

As part of the TSP process, Cascade convened the Water Connections Working Group to provide community and stakeholder input into the development of the Cascade TSP.

Figure 1 - Cascade Service Area: Click to Enlarge
Cascade Service Area

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 also administers regional water conservation services on behalf of its members. The 2008-2014 Conservation Program has a goal of achieving water savings of 1 million gallons per day (mgd) in terms of annual average consumption and 1.45 mgd during the peak season. By the end of 2010 the annual average goal had already been attained. From 2014 through at least 2020 Cascade anticipates continued conservation activities.