With less and less fresh water being available (due to climate change, overuse and pollution), and salt leaching into water in arid regions (salinisation), there is a need to find a solution to the potential water shortages that we are faced with.
One such solution that has been implemented in many places is desalination.
What is desalinisation?
Desalination is the process of removing salt and minerals from water. Typically, ocean water is used and desalinated to provide fresh water for drinking.
Ocean water generally contains 35,000 parts per million (ppm) of salt, compared to freshwater, which contains less than 1,000 ppm.
Globally, 14 million meters3 per day of freshwater is made. However, this still only makes up 1% of total world consumption.
How does it work?
There are two main methods, the distillation method, and the reverse osmosis method.
The distillation method harvests freshwater from the steam of boiled water. The more common modern technique is reverse osmosis, where water is passed through a membrane, and as salt molecules are larger than water molecules, they are filtered out.
Where is it occurring?
Desalinisation is often used on ocean going vessels such as ships and submarines. 120 countries around the world have constructed desalinisation plants. 70% of water desalination occurs in the Middle East, and 6% in North Africa. The difference is made up by countries such as The USA, China, and Australia.
Kwinana Desalination plant in Perth
The Perth Seawater Desalination plant was completed in 2006, and produces up to 45 billion litres (gigalitres) of drinking water per year, using the reverse osmosis method. Overall, this is 17% of the city of Perth’s supply. A second desalination plant was completed in 2011, and it is currently being expanded to produce up to 100 gigatones of water per year by the end of 2012.
But its not without its drawbacks…
Desalinisation is very energy intensive, therefore is very expensive. This makes it a less appealing option than traditional freshwater sources such and groundwater extraction or riverwater. Most desalinisation plants use either fossil fuels or nuclear power (both of which have obvious negative implications).
Places which are under water stress are often not located at places where desalinisations is possible (places very high in altitude or very far from the sea). Therefore, transport costs often incresase the overall cost to make desalinisation untenable.
Desalination affects marine life. When water is drawn from the sea, all the small creature in it also come along, including plankton, fish eggs and fish larvae.
Furthermore, the by product of many desalinisation techniques is a heavy brine, which is often returned to the sea, where it may sink to the bottom and cause damage to ocean floor ecosystems.
While desalination may be a savoir in many places in the future, the cost is still high, and there are still negative impacts. In the short term, water conservation is still the most cost effective way to get the most out of this precious resource. You can find out more about your own water footprint here.
U.S Geological Survey, Water Science for Schools.
National Geographic, Could Seawater Solve the freshwater crisis?