Hydrogeologically, Rapa Nui (Easter Island, Chile) is one of the least understood islands in Polynesia. There are no surface streams, the soils are poor in productivity and highly permeable, and the water table sits far below the surface of the island. One of the many mysteries of Rapa Nui is how the ancient inhabitants survived with so few sources of freshwater.

Fieldwork was conducted to identify terrestrial sources of freshwater and to evaluate the occurrence of submarine groundwater discharge (SGD). We documented observable surface water features located in the interior and coast of the island and made field measurements of water temperature and salinity to identify areas of SGD along the coast. The limited number of interior surface water features, periods of drought, permeable aquifers, and existence of puna (dug wells) along the coast of Rapa Nui lead us to conclude that coastal seeps were an important prehistoric source of freshwater.