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.

Seattle Public Utilities Agreement
A contract between Cascade and Seattle Public Utilities (Seattle) for the sale and purchase of potable water was signed in 2003 with an effective date of January 1, 2004. Under the "50-Year Declining Block Water Supply Agreement between the City of Seattle and the Cascade Water Alliance", Seattle is obligated to provide potable water (and Cascade is obligated to purchase it) through December 31, 2053. The quantity through year 2023 is 30.3 MGD on an average annual day basis (additional water is provided during the Peak Season and Peak Month). The amount of water available under this agreement declines in 5 MGD increments every five years, beginning in 2024. For the last 10 years of the agreement, Cascade will receive 5.3 MGD (average daily supply) from Seattle. Water in excess of the amounts listed in the contract may be supplied by Seattle at a surcharged rate. However, Seattle does have the option to refuse Cascade's request for additional supply.

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 for the next decade.

Tacoma Public Utilities Contract
In October 2005, Cascade and Tacoma Public Utilities (Tacoma) executed a contract for the wholesale purchase of water from Tacoma by Cascade. Tacoma's available excess supply will help fulfill Cascade's supply needs beginning in 2008. A portion of the water purchased (4 MGD average daily supply) is permanent supply for Cascade. Tacoma will also reserve an additional 6 MGD (average daily supply) for Cascade through 2026. From 2026 through 2030, the amounts of water reserved for Cascade decline. The contract provides a schedule of minimum annual purchase amounts through 2025. Cascade may request additional water if Tacoma has excess supply available.