|Fig. 1: Modern Water's containerized forward osmosis desalination plant, located at Al-Khaluf in Oman. (Source: Wikimedia Commons)|
The Middle East is one of the driest places on the planet. Average rainfall ranges between 20-40cm per year compared to 72cm globally and droughts are frequent in the region.  The region is also experiencing a rapid population growth where population has increased almost three times in the past four decades.  For these reasons and others such as poor water management, water resources are becoming increasingly scarce. Water desalination has been practiced for more than 50 years in the region and has become the primary response to water shortage in several countries. The region accounts for almost half of the global desalination capacity with Persian Gulf states having the largest share. 
There are three main methods of desalination namely thermal, electrical, and pressure.  These methods differ in terms of energy consumption, cost and whether they can be used for seawater or brackish water treatment. The three most common desalination technologies in the region are multistage flash (MSF), reverse osmosis (RO) and multi-effect distillation (MED). MSF and MED are distillation-based plants, whereas RO uses membranes to separate salts from water.  Historically, distillation technologies have dominated the seawater desalination market, partly because they lend themselves well to co-generation of water and power.  Recently, global share of RO has increased owing to the development of better membranes and reductions in energy consumption. By 2008, RO accounted for 53% of worldwide capacity while MSF consisted of almost 25%. While MED is less common than RO or MSF, it still accounts for a significant percentage of global desalination capacity. 
In the Middle East, thermal technologies are mainly used by oil rich countries neighboring the Persian Gulf where energy prices are low. These countries include Saudi Arabia, Kuwait, UAE, Qatar, Oman and Bahrain with a total installed capacity of around 26 million m3/day by 2008.  Saudi Arabia is the biggest producer of desalinated water where more than 70% of its water needs are satisfied by desalination. Other countries in the region lacking domestic fossil fuel energy sources, have their major plants built for membrane technologies which are less energy intensive and only require electrical power as energy source. These countries rely less on desalination due to financial restrictions and better access to other freshwater resources.
Cost is the biggest challenge with desalination. A study estimated the cost of desalinated water per m3 to be 1.04, 0.95 and 0.82 USD for MSF, MED and RO assuming a fuel cost of 1.5 USD/GJ.  Energy accounts for approximately 75% of the supply cost of desalination.  One should also add water transportation costs and environmental externalities to the overall cost. This makes desalination less attractive for poorer countries in the region.
Desalination can have significant negative impacts on the environment. One impact is the discharge of salt on coastal or marine ecosystems in the case of seawater desalination. Plants treating brackish water can pollute rivers, aquifers and soil. This is of increasing concern in the Persian Gulf since it is a small and enclosed sea and considerable amount of desalination takes place on its shores. Salt harvesting can potentially be used to both reduce the environmental impact of plants and offset the total cost of desalination.
© Yashar Rajavi. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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