How Does Desalination work?

Only a tiny fraction of the planet’s water is fresh. After subtracting ice caps and glaciers, the amount gets substantially smaller. Since humans need water to drink and to sustain agricultural production, people have always looked to the ocean as a potential solution for water shortages.

Because it requires so much energy, desalination has long been considered far too expensive to be a viable large-scale option. Thanks to advancing technology, however, it’s become more realistic, prompting many American communities to invest billions of dollars in full-scale desalination facilities.

The Process

There are several ways to separate salt from water. However, producers usually rely on reverse osmosis and multistage flash. With osmosis, salt water is forced through a semi-permeable membrane. Under the influence of considerable pressure, water molecules move through the filter, leaving larger sodium molecules behind.

With multistage flash, large amounts of heat are used to convert salt water into fresh water. The term “flash” stems from instances where the water is brought to a boil throughout various stages of the process. As the salt water is subjected to externally supplied heat in each stage, evaporation occurs and fresh vapor is collected.

What’s Holding Back Production?

If desalination is a reality, why aren’t more plants quenching their thirst around the world? Right now, desalinated water accounts for only around two-tenths of one percent of the fresh water consumed throughout the globe each day. This is largely due to the incredible amount of energy required to fuel desalinization production.

For many cash-strapped communities, this financial burden is too much to bear. That being said, in California, where drought conditions have reached historic levels, a handful of communities are biting the bullet and investing millions to billions of dollars in new desalinization facilities. While this will lead to substantial ongoing costs initially, there’s reason to think these expenses might decline down the line, thanks to emerging technologies that allow plants to produce salt-free, potable water without consuming so much power.