Bench-scale survival studies with Cryptosporidium parvum were conducted with representative aquifer and reservoir waters of Florida. C. parvum inactivation rates ranged from 0.0088 log(10)/day at 5 degrees C to -0.20 log(10)/day at 30 degrees C. Temperature, surface water or groundwater type, and the interaction of these factors had statistically significant effects on the survival of C. parvum.