Desalination is the process by which saltwater is turned into fresh drinking water. The first commercially viable desalination plants were opened in the 1960s. Today there are more than 20,000 plants worldwide. With thousands more plants planned over the next few years, ecologists are worried about the impact desalination is having on our oceans.
A Quick and Dirty History of Desalination
A little known fact is that the third president of the United States, Thomas Jefferson, is attributed with inventing the desalination process in 1791. While building a plant and processing thousands of gallons of water a day was not feasible at that time, all ships carried a copy of the process in case of emergency.
The first commercial desalination plant opened in 1881 at Tigne, Sliema, Malta, followed by several small plants constructed in the Middle East in the 1930s. Each of these early plants could produce up to 6,000 gallons a day of drinkable water. It wasn’t until 2005, when a mega-plant opened in Ashkelon, Israel producing over 87,000 gallons a day, that desalination could be seen as a viable, sustainable solution to the world’s fresh water shortage. Today there are plants around the world that, together, produce tens of millions of gallons of drinkable water a day. 
There are two basic desalination processes. The thermal process heats up the water and the captured condensation is suitable for human consumption. The second process is reverse osmosis (RO), where the seawater passes through a membrane that blocks salt molecules but allows the passage of the smaller water molecules.
Effects of Desalination on the Environment
The majority of desalinated water today comes from RO plants. Two gallons of seawater is used to produce one gallon of drinkable water and the remaining sludge is returned to the sea. If not properly diffused, this briny sludge can cause serious damage to the ocean life, cutting off the oxygen supply to plankton, fish eggs and larvae, and other microbial organisms. The sludge is also toxic for humans so swimming and bathing must be prohibited in the vicinity of the desalination plant. 
In addition, many chemicals are used as a pre-treatment for desalination including chlorine, hydrochloric acid and hydrogen peroxide. There have been cases where large amounts of these chemicals were not only found in the ocean, but actually passed through the RO process and were found in the drinking water. 
However, the biggest problem to date with desalination is the huge amount of energy needed to produce drinkable water. There is no doubt that the greenhouse gas emissions caused by the fossil fuels used to operate the desalination plants are a serious contributor to global warming, especially in the Middle East. 
The Final Note
Though the cost of desalinated water is about half of what it was just a couple of decades ago, it is still more expensive than pumping water hundreds of miles. However, with the world’s fresh water sources disappearing at a frightening rate, desalination is a necessary alternative as a fresh water supply. To date there are 300,000,000 people around the globe whose main source of fresh water is desalination.
Saudi Arabia uses 20% of the world’s desalinated water. Rich in fossil fuels and financially able to absorb the high costs of desalination, desalination is a great solution for Saudi Arabia and countries like it. However, the cost to the environment is heavy and long-term.
There are pilots underway for operating desalination plants using solar power. This would be a major step forward not only in cutting costs but also in minimizing the huge environmental footprint of today’s desalination plants. In addition, regulatory steps can and must be taken before a desalination plant goes into production to ensure that no unnecessary chemicals or brine are dumped into the seas or other places where they could contaminate freshwater tables.
It seems that we never have time to do a job right but always have time to do it twice. If we overcome this human weakness and work smart from beginning to end, desalination can be an important and environmentally safe drinking water solution in arid countries and regions like South Africa, Australia, California and the Middle East.
 Matt Mazur, Desalination Plant History, 2019
 Scientific American The Impacts of Relying on Desalination for Water, 2019
 Carrie Terry, The Disadvantages of Desalination Plants, April 19, 2018
 Jim Robbins, Desalination is Booming as Cities Run out of Water, June 27, 2019