Evapotranspiration is the process of water moving from the land to the atmosphere through evaporation and plant transpiration. It's important for balancing water levels, but it's hard to measure accurately. The article discusses how to estimate crop evapotranspiration for irrigation and farming. They use a two-step method involving crop coefficients and reference evapotranspiration. The Penman-Monteith approach is used to calculate reference evapotranspiration. Tables show crop coefficients for different crops and regions. The article also explains how to improve crop coefficient estimates. Overall, the article provides methods for estimating water needs for crops and managing agricultural water effectively.