The source of freshwater for Tonga is either through rainwater harvesting, or extracted from a thin freshwater lens within the highly porous limestone substrate. The water resources of Tonga are primarily in the form of groundwater. Surface water resources are not present on most islands; exceptions are 'Eua where supply originates from springs in caves high above sea level, and on a number of the volcanic islands including Niuafo'oua and Niuatoputapu and Tofua, where there are several salty lakes.
Surface water: Eua, Niuafo'oua and Niuatoputapu and Tofua.
Groundwater: Urban centres.