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Portland Water Bureau

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Weekly Watering Number – An Evapotranspiration Transformation

By Lindsay Wochnick

Signs of summer – browning lawns, wilted plants, and dry soils – have appeared early this year, and many Portlanders have responded and started to water lawns and gardens.

Weekly Watering Number When watering, it can be hard to know how much to use. Plants lose water through a process called evapotranspiration (ET) which is the combination of water lost through evaporation and from plant transpiration. Generally, the amount of water lost through ET is equal to the amount of water that must be replaced to maintain healthy growing conditions. 

The rate of ET is affected by the amount of sun, wind, air temperature, and other variables. In Portland, it generally takes one-inch  of watering each week during the summer to offset normal ET for lawns.

Take the guesswork out of predicting the needs of your plants by looking at the Weekly Watering Number, a service provided by our partners at the Regional Water Providers Consortium which gives you the amount of water (in inches) your plants will need each week. 

The weekly watering number is updated every Thursday from April-September. It takes into account ET rates according to your zip code. Visit  http://www.conserveh2o.org to see what your plants need today!

Sarah Murphy Santner
Water Efficiency

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Spam Prevention In the Pacific Northwest, what state is Portland in?