The subsurface of Tongatapu Island consists of permeable limestones and it is assumed that the average amount of infiltration of rainfall through the semipermeable soil cover into the limestone would be about 1,500 litres per second, equivalent to an average of 280,000 gallons per square mile daily. From the data available, it was possible to prepare a sketch map of the groundwater table, showing that the fresh water table is generally less than two feet above mean sea level. From present data it is possible to say that the recharge rate of the subsurface aquifer from rainfall is more than enough to supply the whole of the present population and also to irrigate parts of the island from groundwater sources; however, careful and continuing studies and observations of the groundwater conditions will have to be made constantly in the future, particularly if the demand for groundwater increases, as will most likely happen. Good locations for constructing new wells are west of Nuku'alofa and in the area of the airport.