Aquatic resources are used extensively by many human populations but their role in the ecology of other primate species has been understudied. At least 10% of extant primates interact with aquatic environments, and a more complete understanding of these interactions is needed to get a complete view of primate behaviour. Five major factors appear to most strongly influence primate water use: thermoregulation, display behaviour, range, diet and predation. The ecological and evolutionary implications of these factors are discussed for extant primates as well as the possible influence of water on hominin evolution.