The Washington State Department of Ecology on Thursday granted the Cascade Water Authority the approval to use a portion of Lake Tapps water as a future drinking source.

This will be the first regional water supply to come on line in the Puget Sound area in many years.

The decision also guarantees summer recreation levels for one of Pierce County’s most popular lakes and robust flows in the White River that support habitat and salmon runs while improving the river’s water quality.

“The work to decide who gets to use the public’s water is some of the most difficult we face at Ecology,” Ecology Director Ted Sturdevant said in a press release. “I believe we’ve struck the right balance with this decision. The key interests of each party have been preserved, reflecting the art of compromise necessary for good water decisions.”

Pierce Councilman Shawn Bunney and state Rep. Chris Hurst, two of those who have been actively involved in negotiations, agreed.

“Although the devil’s always in the details, I think we have a good proposal and am pleased that we may soon see a successful end to this process that has now lasted over a decade,” Bunney said.

Cascade is a consortium of eight municipalities and provides drinking water to nearly 400,000 residences and more than 22,000 businesses in eastern King County.

The finalization of these rights completes a decade-long effort to identify and develop a way to preserve the Lake Tapps reservoir from drying up.

Lake Tapps is a reservoir created in 1911 as part of a hydroelectric project on the White River. When Puget Sound Energy announced in 1999 it might not have the ability to continue operating the system, concerns arose about the lake’s future. Lake Tapps community homeowners and others who enjoy the lake were particularly worried about maintaining appropriate lake levels for swimming, boating and other recreational activities.

Proposals emerged in the early 2000s to save the lake by turning it into a drinking water supply. Puget Sound Energy ended the hydroelectric operations in 2004 but agreed to keep the lake filled while negotiations to sell the lake were ongoing. Cascade purchased Lake Tapps from Puget Sound Energy in December 2009.

The work to secure four new water rights and to transfer another has been a lengthy and complex process, requiring thorough environmental scrutiny. It involved negotiations with many stakeholders, including Cascade, the Muckleshoot and Puyallup tribes, the Lake Tapps Community Council and four other neighboring cities.

“I would like to see the fine print, but it seems that we are finally at the end of this long journey with an agreement which protects the lake, citizens of Lake Tapps, fish and a regional water supply for the future,” Hurst said.

Ecology’s decision gives Cascade the right to eventually divert up to 48 million gallons of water daily from Lake Tapps to serve its customers. Cascade agreed to prioritize specific flows in the White River and summer recreation levels in Lake Tapps ahead of taking water for municipal use.

Cascade does not plan to develop this regional water supply for decades, and will still have to build water treatment and delivery systems.

Ecology’s decision is final pending any appeals which must be filed within the next 30 days.