Water resources in Saudi Arabia include surface water, underground water and unconventional sources including desalinated sea water and treated sewage water.

Surface Water Resources:
Rain is a renewable water resource. Annual average rainfall in the Kingdom is around 100 mm and the southwestern region has the highest rainfall amounting 250 mm annually. To make use of the rainwater, the Kingdom has built 214 dams with 25 under construction and nine were announced for tender. The storage capacity of the largest dam, King Fahad bin Abdulaziz dam at Bisha is 325 million cubic metre and Najran Dam 86 million cubic metres. Total storage capacity of the entire kingdom's dams is 810 million cubic metres.

Underground Water Resources:
There are two types of underground water resources, Deep and Shallow. The deep underground water is found in the successive geologic layers dating back from the Cambrian age to the Present and the age of the trapped water there ranges between 15 and 35 thousand years. Average rainwater supply to these Deep Underground water resources is very little and much less than the annual water taken out of them. The depth of the water in these formations ranges from 100 to 2500 metres. The Shallow Underground Water resources are renewable and are supplied directly from rainwater. Their depth ranges from a few metres to 100 metres. These water resources make up 50% of the water designated for human consumption and about 100% of the water used for cultivation.

Desalinated Sea Water:
There are 30 desalination plants on both red Sea and the Arabian Gulf. The capacity of these plants is 994 million cubic metres. These plants also produce electricity.

Treated Sewage Water:
About 60% of the water consumed by the people is treated as sewage water. Some is tertiary treated as safe water and some is doubly treated that could be used for agricultural and industrial purposes to reduce the consumption of the other water resources. One third of the daily sewage water, which is estimated about 1.3 million cubic metres, is tertiary treated.

Wetlands
Wetlands are both an important component of the water resources of the country as well as being key areas of biodiversity. Both natural and artificial wetlands are important habitats for many species. Perennial wetlands are the only habitats in which freshwater fish can survive; perennial and ephemeral wetlands are also critical for the survival of frogs and toads, dragonflies, and freshwater molluscs; they are also nationally and internationally important breeding and resting sites for resident and migratory birds, as recognized by the Bonn Convention for migratory species, which seeks to protect and /or restore wetlands as critical habitats for wildfowl and other migratory birds.

Saudi Arabia's natural freshwater wetlands, including ponds, perennial streams, and springs, are small both in number and in extent; because water is so scarce and valuable a resource in arid lands, they are also extremely vulnerable to agricultural development through drainage, settlement, overgrazing, over hunting, and overuse by visitors. Pumping for irrigation has already drained Uyun Layla, a cluster of karstic ponds that included the Kingdom's largest perennial body of fresh water.

Artificial wetlands, such as reservoirs, irrigation drainage, and sewage outflows, are an important factor in the sudden increase in diversity of migratory birds recorded at many sites in the Kingdom. But they are largely an ephemeral by-product of municipal and agricultural projects, in which wildlife conservation will have to compete with other needs such as the re-use of waste waters for domestic and agricultural purposes. Hence the management of most artificial wetlands belongs properly with the Ministry of Electricity and Water, and the Municipalities and related commissions and the NCWCD has an advisory role. Unfortunately, many of the larger artificial wetlands are more or less severely degraded through pollution and mismanagement. It is also likely that improved efficiency of use of water by the agricultural and industrial sectors, which must be effected in the future, will inevitably reduce the extent and possibly numbers of artificial wetlands. Such a development is entirely necessary as a part of a strategy to reduce water wastage.