Cotton crop water needs were studied using simple weighing lysimeters to measure evapotranspiration. The researchers built electronic lysimeters costing $1700 each to collect daily data on cotton water use from 2003 to 2006. They found that cotton water use varied between 2 to 8 mm per day, with different patterns each growing season due to changing conditions. This information helps in scheduling irrigations and improving water use efficiency for cotton crops.