This model estimates irrigation water demand for crops based on a crop coefficient and assumed reference evapotranspiration (ETo) under standard conditions. It is assumed that the crops are growing in large fields under excellent agronomic and soil water conditions. This model calculates the crop coefficient (Kc) for all crops in the "crops" array label set, which can be changed by the user. Crop evapotranspiration (ETc) is the product of ETo and Kc. Furthermore, total water demand is ETc divided by assumed irrigation efficiency. The model is loosely based on the guidelines published in the FAO Irrigation and drainage paper 56.