Bermuda has many hydrogeological characteristics which are typically associated with small limestone islands. Only the very oldest of the Pleistocene formations, however, have had time to develop typical karst features, such as caves. The youngest rocks of Bermuda are partially cemented, sandy limestones with high inter-granular porosity and relatively low permeability. Thus, it is in these younger formations that significant fresh ground water lenses have been able to accumulate (see map below).

Consistent with the Ghyben-Herzberg principle, the lenses float in the sea water almost entirely below sea level. Their maximum thicknesses range from 3m (10’) to 10m (33’). They have been developed for water supply purposes, through wellfields operated by the Bermuda Government and private water companies. Following treatment by reverse osmosis, this ground water is delivered to the public via a limited network of “mains” pipelines and by “water truckers”.