Posted January 26, 2010
For most of us, knowing how much water we use is a simple matter of opening the bill that arrives in the mail every month, but state and regional water managers have a far greater challenge. For water managers, water is used only when it is permanently removed from the ground or rivers. The water we use in our houses goes through the sewer and a treatment facility and back into a river or the ground where it can be re-used. For a water manager, the only time water is consumed is when it evaporates into the air or is soaked up by plants and then turned into water vapor (transpiration). Under this definition, measuring water use comes down to measuring evaporation and transpiration, or evapotranspiration.