Agriculture consumes the most fresh water of any other sector. Globally, agriculture is responsible for an average of 70 percent of fresh water consumption; in some countries, that figure jumps to 80 to 90 percent. Given the forecasted global population increase, the agriculture sector will have to produce 70 percent more food by 2050, according to estimates from the Bonn 2011 Conference: The Water, Energy and Food Security Nexus. This will stress water resources even further. Governments worldwide, facing a possible water crisis in arid regions, are searching for options to ensure a reliable water supply for agriculture, and desalination is one of those options.
Desalination for drinking water is a well-established technology. The International Desalination Association counts more than 10,000 desalination plants around the world, 99 percent of which are small scale projects. Many of these projects are implemented under public-private partnerships (PPPs), but most are established as engineering, procurement and construction projects. Most plants are located in Algeria, China, Kuwait, Saudi Arabia, Spain, United Arab Emirates, and the United States. The most active private firms in the desalination market include Doosan, General Electric, Hyflux, Suez, and Veolia Environment.
During the last several years, important technological improvements have significantly lowered energy requirements—the primary operating cost. In the early 1970s, desalination plants consumed more than 20 kilowatt hours of electricity per cubic meter. Currently, desalination plants consume between 3.0 and 4.5 kilowatt hours of electricity. At this rate, the cost of desalinating water per cubic meter ranges between $0.75 and $1.25 for seawater, according to the International Desalination Association.
Wider use of salt water for irrigation would free freshwater for other uses and increase food security for people living in dry coastal areas. As Wired reported in 2010, a British company has developed a low-cost irrigation system that allows saline and brackish water, which contains more salinity than freshwater, to be used for growing crops. The Dutyion Root Hydration System uses a network of underground pipes to deliver water directly to a plant’s roots. Water then diffuses through the walls of the polymer pipe because of differences in moisture levels, which act as filters and leave contaminates behind. Almost any water source can be used—even industrial wastewater—without the need for secondary purification.
As always, environmental costs also need to be taken into consideration, especially air pollution and greenhouse gas emissions for large desalination plants. There may also be damage to marine life due to the pumping of seawater into the plant and discharge of residual salts and minerals.
At its current price level, desalinated water is still not economically viable for most agricultural use, considering the tremendous amount of water necessary for food production (1,300 and 3,400 liters of water required for one kg of wheat and rice, respectively). However, desalinated water has become more affordable for high value crops such as fruit and citrus products, which are less water-intensive (13 and 50 liters of water required for one tomato and one orange, respectively).
While the experience with desalination for agriculture has so far been limited to some projects in Israel, Spain, and high-income Middle Eastern countries, several projects are currently under consideration in low- and middle-income countries. In Morocco, for example, the government is planning a PPP to build a new desalination plant in the Chtouka region to provide water for high-value crops. (IFC is the project advisor.) In Chile, a private firm has proposed to develop a 2,000 ha unoccupied government-owned agricultural land, combined with a desalination plant, under a PPP in Llanos de Caldera. The land would be rented to farmers, who would then pay for desalinated water to be used in irrigation.
Though desalination for agriculture is still at an early development stage, technological improvements leading to lower-cost solutions may make it a more viable option to ensure a reliable water supply for agriculture. For the foreseeable future, however, desalination will remain limited to high-value crops.