Saving Water Partnership

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Get daily updates when the Irrigation Index changes, and/or get weekly updates of the watering forecast:
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Get up-to-date weather data

Find out how much water your lawn needs in real time! Get irrigation requirements and see up-to-date weather data for your area from the Puget Sound Weather Stations.

Calculate how much to irrigate your landscape

Use the Water Budget Calculator to determine how much water a lawn needs, based on the size of your irrigated landscape and yearly weather averages for the Seattle area.
Use the Sprinkler Scheduler to create watering schedules for automatic in-ground irrigation systems, based on the types of your plantings and watering system.

Yesterday’s ET in the Seattle area: 0.12"

ET (Evapotranspiration Rate) is how much water your plants use—thus, how much water you need to replace to keep your landscape green. Watering more than this is a waste of money and water.

Raw Data

Users who need access to weekly raw ET/rainfall data in CSV format can download the data by clicking here.

Please note:
irrigation is not needed in the Seattle area during the months of October through March.
Average ET, Actual and Effective Rainfall and Irrigation Index (for the irrigation season)
Month ET Actual Rainfall Eff. Rainfall (33%) Irrigation Index
April 2.38 2.87 0.89 53%
May 3.14 2.60 0.86 70%
June 3.50 2.00 0.66 78%
July 4.46 0.52 0.17 100%
August 3.71 1.11 0.37 83%
September 2.54 1.29 0.43 57%
Totals 19.73 10.24 3.38  


Year to Year Water Use Comparison Chart

How did plant water use (ET) in 2012 compare to the average for the Puget Sound area?

The table below shows how much water your plants used (ET) in 2012 compared to the average.

Plant water use was down 4% in 2012 compared to the average.

Month Avg. ET 2012 ET ET Diff. ET Diff. % Avg. index 2012 index
(compared to
average)
April 2.38 2.45 0.07 2.9% 53% 55%
May 3.14 3.50 0.36 11.6% 70% 78%
June 3.50 2.92 -0.58 -16.6% 78% 65%
July 4.46 3.63 -0.84 -18.7% 100% 81%
August 3.71 3.89 0.18 4.7% 83% 87%
September 2.54 2.66 0.12 4.6% 57% 60%
Total 19.73 19.04 -0.69 -3.5%    

Changes in plant water use (ET) as compared to the average*
  2005 2006 2007 2008 2009 2010 2011 2012
  Up 5% Up 11% No Data Down 4% Up 6% Down 5% Down 9% Down 4%
*Data rounded to nearest whole number


Past Year's Data


* Note
As with most technology, weather stations and the technology that ties it all together, are sometimes victims of malfunctions. Occasionally the weather data produced and posted on this site might be temporarily inaccurate. Please check the data being used for obvious errors. (for example: if the ET one day is .13" and the next it is 300" then caution is advised)