This document discusses water requirements for different crops and related issues. It provides information on crop water requirement (CWR), which includes evapotranspiration (ET) and other unavoidable losses. For rice, the CWR also includes seepage and percolation losses. The document discusses methods to estimate reference evapotranspiration and crop coefficients to calculate crop ET. It provides crop water requirements and irrigation water requirements for various crops including rice, wheat, maize and potatoes in Bangladesh. The document also discusses effective rainfall and methods to calculate irrigation water requirements.