Cascade currently utilizes a combination of local groundwater supplies and regional supplies purchased on a wholesale basis to meet the water needs of its members. The local supplies are owned and operated by Cascade members. Cascade has entered into long-term wholesale water purchase contracts with Seattle Public Utilities and Tacoma Water.

In late 2008, Cascade and Seattle Public Utilities approved amendments to the 50 Year Declining Block Agreement effective January 1, 2009. Under the amended Agreement, the Cascade Block will be increased by 3 million gallons per day (MGD) from 2009 to 2017 and 5 MGD from 2018 to 2023. This supplemental supply will provide for the projected demands of Cascade members and for the next several decades.