Studies warn area water will get more scarce

Warmer weather and smaller Cascade snowpacks will shrink water supplies by as much as a quarter for Seattle and surrounding areas in the future, according to new studies.

The studies by the water utilities of Seattle, Everett and Tacoma, and the University of Washington, foreshadow a future of dwindling supplies of water divided among competing needs, including a growing population that flushes toilets and waters lawns, and salmon that also need cool water to survive.

Water managers in Seattle, Tacoma and Everett all said they can tweak their systems to assure there's enough water over the next 40 to 50 years. But that hinges on fast-growing Eastside cities like Bellevue finding another source of drinking water.

And in the remote future, climate change, coupled with population growth, could require more dramatic steps such as building plants to recycle water.

"We could use water even more efficiently, and I would love to see that before we turn to new sources," said Richard Palmer, a University of Washington engineering professor who helped build some of the computer models for the research.

"But at some point if population doubles in this region, there's not sufficient stored water right now to meet double the demand."

Palmer cautioned, however, that the full impact of global warming in the region hasn't been gauged. Smaller utilities or areas outside King, Snohomish and Pierce counties weren't covered by the studies. And the research didn't examine how water supply from wells could be affected.

The studies found that by 2075 the three utilities together could lose as much as 77 million gallons a day compared with today's water supplies.

That's an overall drop of more than 16 percent.

Seattle would take the biggest hit — losing as much as 25 percent of its water supply, or nearly 43 million gallons per day.

Seattle is more vulnerable because it relies almost entirely on water from rivers, rather than groundwater.

Those rivers won't be able to fill reservoirs quickly while enough water volume is left flowing for fish, Palmer said.

In comparison, Tacoma would lose as much as 8 percent by 2075 and Everett would see up to 13 percent of its supplies vanish.

Seattle is already working to change how it operates its reservoirs to get more water out of them, said Paul Fleming, manager of climate-change initiatives for Seattle Public Utilities.

That includes putting more water into two Cedar River reservoirs and taking more water from behind the dam on the south fork of the Tolt River.

"We've got these buckets, and we're trying to use more of the buckets," Fleming said of the reservoirs.

Seattle officials predicted that should be enough to meet demand in 2050, even under the worst-case scenario they considered.

But farther into the future, in 2075, the city predicts it would will have to resort to other measures such as more-aggressive water conservation or finding more water supplies.

Even for 2050, however, Seattle is banking on extra water that would be freed up by Eastside cities creating their own water utility and weaning themselves from Seattle-supplied water.

The group, called the Cascade Water Alliance, wants to use Pierce County's Lake Tapps as a drinking-water reservoir.

It has agreed to cut back its future use of Seattle water from 30 million gallons a day to just 5 million gallons.

Warren Cornwall: 206-464-2311 or wcornwall@seattletimes.com