About two-thirds of Israel’s annual fresh water potential are derived from the three major reservoirs: Lake Kinneret (the Sea of Galilee), the coastal aquifer and the inland, mountain aquifer (Yarkon-Tanninim). Lake Kinneret, Israel’s only natural surface storage reservoir, has a utilizable water yield of about 470 MCM, the Yarkon-Tanninim aquifer has a total safe yield of about 300 MCM while the coastal aquifer has a total safe yield of 240-300 MCM. The remaining aquifers are more limited in size and are generally exploited locally. They include an aquifer of Cenomanian-Turonian age underlying the western slopes of the Galilee Mountains, basalt aquifers in the eastern and lower Galilee, a group of small aquifers in the Carmel Mountains and local aquifers in several parts of the Aravah and Negev (Figure x).
The coastal aquifer extends over 120 kilometers of Israel’s Mediterranean coast; its width varies from 3-10 kilometers in the north to 20 kilometers in the south. It is composed of sandstone and sand layers of Pliocene-Pleistocene age. The mountain aquifer is named after its two main natural outlets: the Yarkon Springs, which rise 15 kilometers east of Tel Aviv, and the Tanninim Springs, 60 kilometers to the north. It consists of Cenomanian and Turonian dolomite and limestone rock strata, dipping from their outcrops in the highlands of the West Bank mountains in the administered territories to depths of a few tens to a few hundred meters below the Eocene foothills and the Pliocene-Recent Pleistocene coastal plain.
Israel’s renewable water resources equal approximately 1,600 MCM per year, with an additional 240 MCM added through effluent reuse and some 40 MCM from collection and storage of storm runoff. Total river flow accounts for somewhat over one-third of the total, of which 90% comes from the Jordan River basin. Northern tributaries to the Jordan River, which deliver approximately 520 MCM to Lake Kinneret, come from Lebanon (the Hasbani River), Israel (the Dan Springs) and the Golan Heights (the Banias River and Hermon Spring). Based on this annual inflow, some 470 MCM per year are withdrawn through the National Water Carrier the main distribution system for water from the lake to the south of the country.
Lake Kinneret, which divides the upper and lower portions of the Jordan River system, is the only fresh water lake in Israel. It has a catchment area of 2,730 square kilometers; its area is 170 square kilometers; its maximum depth is 43 meters; and its maximal volume is about 4,300 MCM. The water level, fluctuating in accordance with its use in the national water system and the amount of precipitation and inflow, varies between 213 and 208.9 meters below sea level.
In the lower Jordan River, water flow has been greatly reduced because the water is impounded in Lake Kinneret and the Yarmouk. The quality of water in the lower part of the Jordan is affected by seasonal changes in salinity, especially as a result of the diversion of saline springs away from Lake Kinneret (in order to reduce salination) and due to industrial and domestic effluents.
Israel’s widely dispersed water resources have been consolidated into an integrated water supply network serving all but the extreme southern tip of the country. The 130 kilometer-long National Water Carrier, composed of canals, tunnels, pipes and reservoirs, constitutes the principal leg of this system. While Lake Kinneret is the main surface storage reservoir of the system, water pumped from aquifers and from other sources is added to the main stream of the Carrier as it flows southward. Most of Israel’s regional supply networks are linked to the National Water Carrier, which can transport some 1.4 million cubic meters a day from Lake Kinneret for distribution to coastal areas and the Negev desert. When water demand is low due to rainfall, water from the Carrier is used to artificially recharge groundwater sources. The system thus serves to improve the country’s hydrological situation by making up for seasonal changes.
Since surface and groundwater sources can no longer meet the demands of a growing population and economy, Israel is increasing its development and use of treated wastewater, brackish water and water harvesting
(collection, storage and use of storm runoff).
Israel is a world leader in recycling wastewater, which now accounts for almost 20% of total supply, up from 3% two decades ago. Nearly 70% of the wastewater collected in sewers is treated and reused for agricultural purposes, mainly for the irrigation of non-food crops and animal fodder, in accordance with permits issued by the Ministry of Health. By the end of the century, recycled wastewater may theoretically provide 400 MCM of water per year for irrigation purposes.
Surface runoff in most watersheds in Israel occurs for only a few days a year, after heavy rains. The total mean annual exploitable yield is estimated at 100 MCM per year. Several schemes have been set up for the collection of floodwater, some used for artificial recharge and others as surface water impounding reservoirs. Special techniques have also been developed to harvest water in the arid Negev desert. These techniques involve the construction of small dams and trenches to collect and make optimal use of rainfall and storm runoff. They are used for growing trees and shrubs in areas where rainfall is less than 300 millimeters per year, for halting desertification at the northern edge of the Negev, and for directing rainwater into channels that recharge aquifers.
Brackish water from aquifers is used to irrigate salt-tolerant crops developed in Israel. Israel already uses some 180 MCM of saline water a year for agricultural and industrial purposes. Olive, fig and date trees can tolerate salty water as can broccoli, tomato, spinach, beet and other vegetables, provided sufficient flushing of the salts from the soil is provided.
Due to high costs and energy requirements, seawater desalination may only become a viable option in the longer term. Brackish water, on the other hand, can be desalinated for about a third of the cost of seawater desalination. In Israel, nearly 40 desalination units, used for water supply and research purposes, have been erected over the past few decades with a total capacity of 50,000 cubic meters per day, Of these, 23 plants treat brackish water by reverse osmosis on a commercial basis.
Since 1979, water for Eilat at the southern tip of Israel has been partially supplied by several desalinating units, using reverse osmosis to desalinate water with a salinity level of 6,600 ppm total dissolved salts from a nearby aquifer. In January 1994, a new desalination plant was inaugurated in Eilat with a production capacity of 6,300 cubic meters per day, raising the capacity of all desalination facilities in this area to 27,000 cubic meters per day. These waters are mixed with wellwater pumped from the Paran region, some 120 kilometers north of Eilat.
Cloud seeding provides yet another source of supplemental water, but this technique is expected to provide only a marginal addition to available rainfall.