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Water Accounting Project

How will water availability affect future development in the Methow Valley?  The Water Accounting Project is helping us find out.

The Methow Watershed Council (MWC) is charged with managing our water supply according to the Methow Valley’s Instream Flow Rule (“the Rule”), which sets legal limits on water withdrawal.  The Water Accounting Project is evaluating current and future water use to support the community in creating a vision for the Methow’s future. 

The Rule applies to most single-family domestic use in unincorporated areas in the Methow Watershed.  It limits water withdrawn for those uses to 2 cubic feet per second (cfs) from each of seven river reaches in the Methow basin (“the Reservation”).  Once those limits have been reached, further development would require another source of water.  The seven reaches are: Methow Headwaters, Early Winters, Upper Methow, Chewuch River, Middle Methow, Twisp River, and Lower Methow. 

How are we evaluating water use?

In 2011, the MWC developed the Instream Flow Reservation (IFR) Database to estimate the effects of development on water use and availability in the Methow Basin.  The database was updated in 2019 to account for changes in zoning and new and revised data.  It provides an estimate of water availability based on current zoning and projected build-out. 

The estimates in the IFR Database are based on the MWC’s current water-use estimate of 710 gallons per house per day for indoor, limited irrigation, and stock water use.  Using that estimate, 2 cfs is enough water for about 1,820 houses.

Refining the water-use estimate

The MWC ‘s water-use estimate—710 gallons per house per day—is based on several sources of data, including climatic data, meter data from local water systems water use rates for crops and livestock, and agricultural census data; estimates developed by the Methow Basin Planning Unit; and, aerial photo analysis.  The estimate is also based on use during July—the month during which the largest quantity of water is likely to be used. 

The MWC’s voluntary metering program data will help us better understand how much water local households actually use so we can refine the water-use estimate.

Final Reports

What's next?

The Technical Review Committee and the MWC have approved the Final Report for Task #4. Click here to read the Task #4 Final Report, and here for the Task #5 Report. Next, the MWC will submit the report to Ecology, with recommendations for next steps inducing peer review of the SFD withdrawal number.  You may email the Technical Committee with your questions about the project of for more information.

Smart Meters

The MWC, with the help of volunteer landowners, used smart water meters in a voluntary metering program, to gather data about current use of water in single family domestic wells. Data gathered this summer suggests the current water usage number of 710 gallons per day, consumed, is adequate and accurate to provide to Okanogan County for use in its water tracking database.  The MWC in November 2021, voted to end the metering program after installing 12 meters, and to finalize its report to Ecology this spring. Meters will continue to send data remotely and will continue to help us understand how much water residents use so we can better understand how demand will change over time.

View the first annual Meter Report here.

Go to the Library for more documentation.




Water Withdrawal Study (Part 1, Part 2, Part 3) /2011 IFR Database / IFR Database Update Memo


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