Water does not disappear. It may change its form and possibly its location. There has to be a clear differentiation between "consumptive" use and "withdrawal". These terms apply primarily to surface water (lakes, rivers). Power generation often withdraws large quantities of water (cooling) but return most of it back to the water body albeit degraded (higher temperature). In contrast, irrigated farming withdraws water from rivers and aquifers but the majority is not returned. It is embedded in the plants and moves to the atmosphere via evapotranspiration. Thus, comparisons have to be made on an equitable basis.

Published June 15, 2016 08:34 by Slav W. Hermanowicz, Professor at University of California, Berkeley