Therefore, water should be supplied at the ight amount. Crops should have sufficient water available in the root zone throughout the growing season. This implies crop water requirements which vary during the growing season. For good crop production the irrigation water supply should be timed properly. Irrigation water should be supplied at the right time. In an irrigation project, different crops grow in different parts of the project area, or the same crop is planted at different dates within the same project area. So, irrigation water should be sent to the right place. The goal of imigation is operating the right amount of water at the right time to the right place. To supply the right amount of water, we have to know what is the right amount. Tne factors that determine the amount of irrigation water are evapotranspiration, crop type, rainfall percolation and land preparation. Evapotranspiration is the change of water into water vapor from the water or soil surface into the air(evaporation) and from plants into the air(transpiration). Evapotranspiration(the moth combination of evaporation and transpiration) is influenced by the weather: solar radiation