The main objective was to find the optimum level of water application to Acala Maxxa and Pima S-7 cottons, on sandy soil. The field test consisted of 6 different water application rates through a subsurface drip system on a 2-acre plot. Cutout occurred 4 days earlier for each 10% decrease in the full-canopy pan coefficient, for both Pima and Maxxa. The Maxxa was ready to defoliate 4.8 days earlier for each 10% decrease in the pan coefficient. The driest Maxxa treatment was ready to defoliate 37 days earlier than the wettest treatment. Plant height was found to be a linear function of the total depth of water applied from planting to July 7, with a 2.7" gain in height for every 1" of water applied. The concept of nodes-above-white-flower (NAWF) did not work well for determining the cutout date of the wetter treatments. A slight deficit irrigation treatment was found to produce optimum yields, which occurred at a full-canopy pan coefficient of 74% for Pima and 80% for Maxxa. Maximum yields for Maxxa occurred at a pan coefficient of 94%. The yield on Maxxa dropped off sharply with application rates higher than 105% of pan evaporation. By comparison, the Pima yields did not decrease at all with the wetter treatments; they remained essentially constant for application rates above 100% of pan evaporation. Using a slight deficit irrigation not only saves water, but because of the smaller plants, reduces PIX requirements, and defoliation is much easier. Because of the shorter season produced by deficit irrigation, a generation of whitefly development can be avoided.