How can we measure water when it disappears into thin air? On this episode of What About Water? we’re looking at evapotranspiration, or “ET” for short. It’s the combination of water evaporating from the soil, combined with the measure of water transpiring through crops’ leaves. Accounting for this water loss helps farmers know exactly how much water they should apply across their fields, and new agricultural technologies and satellites are making it much easier.    Jay sits down with California State University at Monterrey Bay Senior Research Scientist –  and former student – A.J. Purdy, whose doctoral thesis looked at the advancement and applications of satellite-derived ET algorithms. We also hear what this looks like in real life, with Brett Baker, a sixth-generation California pear farmer and lawyer. With the ever-present risk of flood on his family’s land in the Sacramento-San Joaquin River Delta, Baker explains how OpenET is helping farmers like him and his father take better measurements of consumptive use.  Robyn Grimm, Interim Director of OpenET, tells us how this open-source platform is making big waves.