Underground aquifers account for more than 70 percent of the water used in the European Union, and are often one of the only – if not the only – source of supply in arid and semi-arid zones (100 percent in Saudi Arabia and Malta, 95 percent in Tunisia, and 75 percent in Morocco). Irrigation systems in many countries depend largely on groundwater resources (90 percent in the Libyan Arab Jamahiriya, 89 percent in India, 84 percent in South Africa, and 80 percent in Spain). Although aquifer systems exist in all continents, not all of them are renewable. For example, those in north Africa and the Arabian peninsula were formed more than 10,000 years ago when the climate was more humid and are no longer replenished.
The aquifers in Africa, however, which are some of the biggest in the world, are still largely under-exploited. They have considerable potential, provided that their resources are managed on a sustainable basis. Because they generally extend across several state boundaries, their exploitation presupposes agreed management mechanisms in order, for example, to prevent pollution or over-exploitation by particular states. Mechanisms of this kind have begun to emerge in recent years. For example, in the 1990s Chad, Egypt, the Libyan Arab Jamahiriya, and Sudan established a joint authority to manage the Nubian aquifer system in a concerted manner. In their project concerning the Iullemeden aquifer, Niger, Nigeria, and Mali approved in principle a consultative mechanism for administering the aquifer system.