Water Planning | Water Supply Portfolio

Water Supply Portfolio

For most of the past decade, conservation programs (including changes to plumbing codes), utility efficiency efforts, lifestyle changes and development patterns have contributed to greatly slowing the increase in water demand. Based on recent trends, the Cascade TSP forecasts the demand for water in Cascade’s service area will remain relatively unchanged through approximately 2020.

For the Cascade TSP, Cascade evaluated a wide range of water supply options to meet long-term needs. These included additional or expanded contracted supplies from existing sources within the Central Puget Sound region; new surface water supplies, new ground water supplies, reclaimed water and enhanced water conservation. From an initial list of 27 possible sources, a preferred supply “portfolio” was selected that includes the following sources:

  • Continued production from member supplies serving their respective service areas.
  • Continued use of water from SPU under the Block Contract.
  • Beginning in 2024, delivery of water from TPU and Covington Water District, which requires construction of additional transmission pipelines.
  • Beginning in 2030 (or as needed) water from Cascade's White River - Lake Tapps Reservoir Project, which requires construction of a treatment facility and additional transmission pipelines.

Under the preferred portfolio, available supplies are expected to exceed Cascade’s forecast water demand throughout the 50-year planning period.

Cascade’s supply planning principles call for maintaining a high degree of flexibility to match available supplies with water needs as economically as possible.

Cascade plans to develop the necessary water treatment and delivery infrastructure in phases over time. While Lake Tapps provides a critical resource for the long term, Cascade will seek opportunities to delay construction of both phases in order to spread the costs of infrastructure development over a longer period of time.

During development of the Cascade TSP, discussions were underway with both SPU and TPU regarding possible changes in the quantity and terms for supply available to Cascade. Changes to Cascade’s wholesale contracts with SPU and TPU have been successfully negotiated. The newly structured contracts do not change the preferred supply portfolio through 2024.

The result of these contract modifications is that Cascade will be able to meet the projected 2040 demands of its members utilizing Member Independent Supply and purchased water. After 2040, Lake Tapps will allow Cascade to meet projected demands beyond 2060. (The portfolios below reflect the modified SPU and TPU contracts and Covington Water District withdrawal from Cascade).

Cascade Supply Portfolio (Average Day)
Cascade Supply Portfolio (Average Day)

Cascade Supply Portfolio (Maximum Week)
Cascade Supply Portfolio (Maximum Week)