the water intake in 45 male (27.50 ± 0.48 kg of mena body weight) santa ines sheep fed with increasing levels (0, 25, 50, 75, 100% dm basis) of prickly pear (opuntia ficus indica mill) to replace corn was studied. a completely randomized block design with nine replications per treatment was used. quadratic behavior was observed for the intake of dry matter, hitting the final weight, which decreased with increasing the cactus in the diet. there was an increase in the intake of natural material and a decrease in voluntary water intake; total water intake increased, and the ratio of intakes: water/dry matter, decreased in the treatment with larger cactus proportion. the pryckly pear constitues a water reservoir for santa inês sheep in brazilian semiarid conditions.