In a Flash

Multi-stage flash water desalination is a process that turns saltwater into drinkable water. Abbreviated as MSF, this process works by using heat exchangers and condensers to turn water into steam, and then back into water. While this method is unfamiliar in the United States, it is the most common drinking water treatment in Saudia Arabia and other desert biomes such as Kuwait and United Arab Emirates.

Image of Saudi Arabia from KPMG.

How does MSF work?

Flash desalination is all about temperature disparity. First, cold seawater travels in pipes through each chamber to the heat exchanger. Pipes are usually zigzagged because it allows for a bigger surface area for the steam to condense on, which means more water produced by the plant.

In the heat exchanger, hot steam heats up the seawater from outside the pipes. The water is then released into the bottom of the first chamber, where the pure water evaporates. Since the pipes bringing in the seawater are much cooler, the water vapor condenses on the pipe system. Freshwater is collected from drops that fall off the pipes.

Down below, the seawater turns into brine as the pure water evaporates and the mineral concentration rises. In the next chamber, the pressure is slightly lower, meaning the boiling point is lower as well. This results in the immediate vaporization of pure water from the surface of the brine, or a “flash”. The process repeats in each chamber as the pressure and temperature decrease. At the end of the process, brine must be reduced to normal sea temperature before being returned to the ocean.

My schematic of the MSF process.

Why does Saudi Arabia use MSF?

Groundwater in Saudi Arabia is located up to 1000 meters below surface. As you can imagine, extensive pipework plunging this far into the soil is no easy feat. Water pressure also becomes an issue with the depth of the pipe systems. Of course, saline water has to come all the way from the Persian Gulf, which makes for a much longer route. Salt water is still a far more abundant and practical resource for the population of Saudi Arabia.

“The Saline Water Conversion Corporation operates 27 desalination stations that produce more than three million cubic meters a day of potable water” – Saudi Arabian Embassy

What are the pros and cons of MSF?

Flash desalination is the predominant form of converting saltwater to water around the world because it is the most efficient. For people who live in dry or desert regions, this technology makes life possible. This process harnesses a virtually unlimited resource and can also be fueled by a renewable resource – solar power.

Flash desalination can be controversial because it produces brine as waste. Brine is water that contains a concentrated amount of certain minerals such as salt. Although brine occurs naturally in the environment, it can have negative consequences when not disposed of properly. Water temperature should also be reduced before disposing of wastewater to prevent thermal pollution.

Saudi Arabian desalination plant from Middle East Utilities.

Another downside to this treatment method is the cost. Countries like Saudi Arabia are rich in terms of oil supply, which provides the energy necessary for flash desalination. Solar desalination could be a way to bring down the long-term cost for other countries, but the initial investment to build a desalination plant is still significant. However, it looks like that is starting to change.

“Israeli households pay about $30 a month for their water…far less than Las Vegas ($47) or Los Angeles ($58)” – Rowen Jacobsen, Scientific American

Leaky pipes are also a consistent issue, regardless of whether groundwater or seawater is harvested. Since the Persian Gulf is 736 km from Saudi Arabia, there are more leaks than there would be with groundwater. According to MIT news, thirty-three percent of desalinated water is wasted due to leaks.

Would you be for or against using MSF to solve the water crisis? Are you more open to living in the desert now that you know clean water is readily available? Let me know your thoughts in the comments below!

Blog at

%d bloggers like this: