How is Seattle’s water supply?

With Governor Inslee’s declaration yesterday of a drought in most of the state, it’s worth taking a moment to look at how Seattle is doing for water resources.

Seattle Public Utilities, which manages Seattle’s water supply and distribution (and for some neighboring cities and towns as well), regularly posts status updates on the water supply, including the current reservoir storage. Here’s the most current status report, from July 12.

The short answer: we’re okay. SPU has about 40 billion gallons of water in active storage, which is almost exactly the twenty-year average amount for this point in the year. At our most recent rate of consumption, that’s over 200 days of water — more than enough to take us into the rainy season.

SPU maintains several reservoirs, which can be filled by shunting water from rivers year-round as appropriate. Seattle’s summer water supply starts as the snowpack in the mountains that accumulates over the winter and spring. The reservoirs are topped off in late spring as the mountain snowpack melts, and then are typically spent down in July through September, Seattle’s dry season.

It may be hard to recall right now, but last winter and early spring were particularly wet and snowy and it led to a much larger than usual snowpack. That gave us an extra two weeks or so of snowmelt runoff feeding our rivers this summer — and is probably part of the reason why our recent extreme heatwave didn’t immediately cause more forest fires.

Overall this year we’ve had a wetter winter and a drier summer (the opposite of 2020), and as of this week we’re back at average total precipitation year-to-date.

SPU has become very adept at tracking precipitation and forecasts, and strategically managing the city’s reservoirs while minimizing the impact to water flows on our rivers (an effort distinct from Seattle City Light’s hydroelectric dams, a subject for another day).

We’re now at the time of the year where the snowpack is gone, the dry season is upon us, and we’re almost entirely reliant on the water in our reservoirs until October. Due to SPU’s good work, we have more than enough water for that period.

Of course, we have no guarantees about how long the dry season will last this year, or how much snow we’ll get in the mountains next winter. So while we’re far from needing to institute emergency measures, we should continue to conserve water wisely. We also need to be “good neighbors” and keep in mind that every other part of the state is now in a drought emergency.

Here’s SPU’s official “everything is fine, don’t panic, but don’t do stupid things” statement on the city’s water supply:

Based on current conditions and forecasts, the Seattle regional area, as well as Everett’s and Tacoma’s service areas, have sufficient water supply for people and fish this summer.  We thoroughly analyze our water supplies regularly – we measure the water level in our reservoirs, how much water customers are using and how much water is flowing into our watersheds. We also monitor weather forecasts and plan for their impact on our water supplies. Over the summer, we will continue to carefully monitor our water supplies. We continue to encourage customers to use water wisely.

As of the last two weeks, however, we’re not doing our part — consumption has shot way up. Yes, it’s been hot and dry, but c’mon folks, let’s get this under control.

I hope you found this article valuable. If you did, please take a moment to make a contribution to support my ongoing work. Thanks!