Water Source

Water Supply Conditions as of August 11, 2022

Our water supply is ample.

Water Supply Indicator

Critical Abundant

How to read the Water Supply Indicator

  • Blue — Abundant: Average to wet year. Surplus water supply.
  • Green — Ample: Near normal conditions. Water supply can meet customer needs.
  • Yellow — Adequate: Slightly drier than normal.
  • OrangeReduced: Water supply is approaching minimum availability; monitor for water shortage response measures.
  • Red — Critical: Water supply reserves are critically low; monitor for curtailment notices.

The Tacoma Water Supply Indicator (WSI) can help inform you about changing water supply conditions. Our water resource engineers developed it to monitor our primary water source, the Green River Watershed. Because conditions can vary significantly from county to county and from month to month, the WSI provides updated water messaging for Tacoma Water customers.

Tacoma Water currently maintains adequate sources of supply to meet out customers’ projected use. Full municipal storage behind Howard Hanson Dam was achieved in June. Peak snowpack was near average and melt off is expected to continue through June. Recent low rainfall and high temperatures have lowered the water supply indicator from wet conditions to near normal.

We continue to recommend Tacoma Water customers use water wisely.


Water Sources

The source of our water supply varies throughout the year, depending on the season, weather, snowpack level, inflows and water storage conditions.

Our Firm Yield is 107 million gallons per day (Firm Yield is the “minimum” amount of water that we can reliably produced on any day of a given year). The average use is approximately 50 million gallons per day (excluding Tacoma’s production for the other three partner utilities in the regional water supply system). Note that our peak use during the summer may be double this average, and exceed our Firm Yield in some cases.

Below is the typical amount of water available by the source:

  • Green River supply – 73 million gallons per day
  • Second Green River supply– 27 million gallons per day on average (interruptible share of regional water supply system; includes storage)
  • Local wells – 40 million gallons per day
  • North Fork wells (alternative Green River supply – not additive to other sources) – 60 million gallons per day

For more information read our Integrated Resource Plan on our ability to manage available water supplies, plan for new supplies as needed, and protect stream flow for fish in the Green River

Customer Impact

We are privileged in Tacoma to have an abundant and consistent water supply from the upper Green River in the Cascade Mountains. Most of the time, can all use water wisely and not be concerned about running low. To help conserve water, we encourage customer to use WaterSense-labeled fixtures and EnergyStar-labeled appliances and fix leaks. We offer a variety of products to Tacoma Water customers to help you find easy ways to instantly save water and money at home (must live in Tacoma Water service area). Outdoors, customers can minimize water use while still maintaining a healthy landscape.

However, sometimes it is drier than usual, and sometimes there are arid conditions. During those times, especially when our water supply indicator is in the red zone, we may ask you to reduce your water use or require you to use less water.

If this happens, we’ll provide plenty of clear communication in advance and place information online, via social media, and our newsletter(s). We’ll include recommendations and offer solutions about what you should and should not do. Updates will also include when we expect to return to stability.

Managing Supply

Our water resource engineers monitor the health of our water supply daily. Multiple agencies also report daily snow depth, snow water equivalent, accumulated precipitation, Eagle Gorge Reservoir storage quantities, and Green River inflow and observed runoff. We compile this into the Water Supply Index model and produce an overall score. These scores are then compared to history (usually 30 to 60 years). We also monitor the weather models from the National Weather Service’s Climate Prediction Center, including temperature precipitation forecasting and weather anomalies such as El Nino and La Nina.

In addition to maintaining adequate supplies for general water use, Tacoma participates in a fisheries resource management group with federal, state, and local jurisdictions to safeguard our native salmon and steelhead species in the Green River. A portion of Tacoma’s storage reserves is used for this purpose each year.

In particularly challenging years, we use the South Tacoma Wellfield to supplement our water supplies. This enables us to reserve adequate storage for augmenting natural stream flows, and maintaining healthy fish habits.

Data Sources and Agencies

We rely on many partner agencies to share their data with us as we analyze our water situation in any given year. You can look at these datasets, too, by visiting the following partner websites:

State of Washington drought information

Green River snow and precipitation telemetry information

Howard Hanson Dam hydrology observations

Green River hydrology information

Long Term Planning

Our Water Supply team is also thinking long-term about what water we need and is available for our growing service area. Rest assured, we are looking as far as 50 years into the future to make sure at that time we still have all the water we need, even in the face of a changing climate. You can read these plans and how we did our analysis in our Integrated Resource Plan.

If we find ourselves in a drought with a water shortage, we have a plan for what to do. This Water Shortage Response Plan includes the steps we’d take to manage our water supply prioritizing public health and safety. It also includes the outline of our communications plan — how we would tell you what is happening and what to expect.

Resources

To learn more about your water supply, see the following pages:

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