Pima and Acala cotton irrigation trials were conducted on multiple fields over the past several years to ascertain crop responses to water deficits under a wide range of planting conditions and soils types. Large scale on-farm and small scale university research and extension center replicated trials were established with water regimes that varied from low stress, full Evapotranspiration (ET) treatments to moderate stress, reduced ET irrigation treatments that were accompanied by significant yield loss. This paper describes how crop water regime influences plant water stress levels and what impacts modest to moderate plant stresses have on plant growth, fruit retention and crop productivity. We present information on soil water availability in the root zone and how it is related to the timing and severity of water stress and factors to consider when establishing irrigation schedules for Pima and Acala cotton.