An outbreak of Cryptosporidiosis occurred among children and counselors at a summer day camp on the grounds of a public elementary school in Florida. Water at the camp was a suspected source of illness. Campers and counsellors had drunk water from outdoor faucets and indoor faucets. Outdoor faucet water samples were positive for total coliforms and Cryptosporidium parvum. Other water sample tests at the school were negative for coliforms, bacteria, and ova and parasites. Contamination of the outdoor faucet water likely occurred at the nozzle of the hose used to fill the water coolers. This faucet had not been protected against fecal contamination. There was no evidence of water contamination at the main municipal source. Water from hoses is particularly susceptible to back siphonage and contamination.