In the absence of permanent rivers or bodies of water, rainfall, groundwater, desalinated seawater, and very scarce surface water must supply the country's needs. In eastern Arabia and in the Jabal Tuwayq, artesian wells and springs are plentiful. In Al Ahsa a number of large, deep pools are constantly replenished by artesian springs as a result of underground water from the eastern watershed of the Jabal Tuwayq. Such springs and wells permit extensive irrigation in local oases. In the Hijaz and Asir, wells are abundant, and springs are common in the mountainous areas. In Najd and the great deserts, watering places are comparatively fewer and scattered over a wide area. Water must be hoisted or pumped to the surface, and even where water is plentiful, its quality may be poor.
Modern technology has located and increased the availability of much of the underground water. Saudi Arabian Oil Company (Saudi Aramco) technicians have determined that very deep aquifers lie in many areas of northern and eastern Arabia and that the Wasia, the largest aquifer in Saudi Arabia, contains more water than the Persian Gulf. The Saudi government, Saudi Aramco, and the United Nations (UN) Food and Agriculture Organization (FAO) have made separate and joint efforts to exploit underground water resources. In the past, improperly drilled wells have reduced or destroyed any good they might have served by leaching the lands they were drilled to irrigate. Successive agricultural projects, many of which were designed primarily to encourage Bedouin settlement, have increased water resource exploitation. In the early 1990s, large-scale agricultural projects have relied primarily on such underground aquifers, which provided more than 80 % of the water for agricultural requirements. In fiscal year (FY) 1987, about 90% of the total water demand in the kingdom was consumed by agriculture.