Urinary excretion of estrogens, including endogenously produced estrogens, estrogens from dietary sources, and estrogens from prescription medications and veterinary pharmaceuticals, can result in surface water contamination and subsequent human exposure via contaminated drinking water. Caldwell et al. predicted average estrogen exposures through drinking water based on estimated levels of per capita estrogen use and excretion by humans, estrogen removal by sewage treatment and other processes, and surface water flow rates.