Oman lies in an arid region; rainfall is limited and irregular over much of the country. Mean annual rainfall in the coastal plains and desert areas is relatively low, less than 40mm. In mountain areas, however, where rainfall is greater, up to 350mm, it provides a source of natural recharge to a number of aquifers including those in the interior and coastal areas. Three prime sources of water have been considered in developing water resources in Oman. Surface water represented by ghaily aflaj, springs and few permanent wadi flows and groundwater as daudi aflaj and wells representing over 70% of the total water usage. Some areas showed severe water shortage due to over-abstraction, in Al Batinah and Salalah coastal areas saline intrusion irreparable damage to the aquifer. Desalination of sea-water which become an important contributor to water supply where natural water resources are unavailable or inadequate.
There are two main types of water resources in the Sultanate; conventional water resources (natural) including surface and ground water that present about (87%) and non-conventional water resources including desalination water and treated wastewater that present about (13%), clarified by the following chart.
The natural water resources comprise two main resources “renewable” and “non-renewable”. The “renewable” resources replenished from rainfall and stored in under groundwater aquifers, the quality of groundwater from aflaj and wells located in the upper reaches of catchments throughout Northern Oman is generally suitable for domestic and agricultural purposes. Groundwater becomes brackish and saline toward the coast, and there is similar deterioration of water quality in the interior particularly in the lower reaches of the wadis. In the Najd (Southern Oman), groundwater occurs within four distinct limestone formations and the water quality within them varies from potable to brackish. Total replenished of the renewable resources is estimated to be about 1.300 M.m3/yr. Recovery level is currently about 70%; the balance is lost through seepage across submarine or national boundaries.
The “non-renewable” resources comprise underground fossil water located at carbonate formations within the Interior basin. The storage is very large but their renewable yields are low and largely restricted to the groundwater throughflow.
Since 1989, the governmental laws and regulations had a very important role in protecting Oman’s water resource either from depletion or pollution. The Sultanate had taken several important actions regarding conservation of water resources, through many progressive regulations in order to control the demands, abstraction and protection of water resources. The following are the most important ones: