The lenses of potable groundwater which exist on small limestone islands are a valuable natural resource and their rational development is considered to be of great significance to the inhabitants. Using the assumption that abstracting groundwater from a freshwater lens is equivalent to reducing vertical recharge, an estimate of the sustainable yield of the lens is made. This estimate is refined by taking into account the amount of storage which must remain within the lens so that abstraction can continue during drought periods and also the reduction of the freshwater head and consequent increase in the thickness of the transition zone brought about during pumping. The most effective method of developing the resource depends on the depth to the water table, the thickness of the lens and the permeability and nature of the aquifer. Boreholes are recommended where lenses are thick and shallow infiltration galleries where the available thickness of freshwater is limited.