What Is Desalination & How Does It Work?

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Water desalination is a type of water treatment that’s used to remove salts and minerals from a water source.

Here, we’ve shared everything you need to know about water desalination and how it works.

πŸ“Œ Key Takeaways

  • Water desalination is when minerals and salts are used from a water source.
  • Desalinated water might be used for drinking or agricultural purposes, or in commercial or industrial applications.
  • Desalination uses an abundant water resource (the ocean) and is reliable and effective, but is costly and uses a lot of thermal energy.

πŸ€” What Is Desalination?

Water desalination is the process of removing minerals and salts from salt water to make it suitable for a specific purpose (usually human consumption or agriculture).

The most obvious example of water desalination is seawater desalination, which involves treating seawater to remove its high salt content and make it safe for drinking.

Desalination isn’t a popular water treatment method, and only a small percentage of water is desalinated for human use.

However, desalination is increasing in population for agricultural use, especially in parts of California.

πŸ‘¨β€πŸ”§ At-home water filters are now available to bring the water desalination process to your own home. Reverse osmosis is the most popular at-home desalination solution.

The desalination process as illustrated by the Public Utilities Board, Singapore
The Desalination Process, via Public Utilities Board (Singapore’s National Water Agency)

🧐 Where Is Desalination Used?

There are several occasions in which desalination might be used, including:

  • For boats that have seawater as the most convenient water supply
  • For residences in certain regions
  • For beachfront hotels and resorts
  • For commercial use
  • For industrial applications

In short, wherever there is a need for water, where it makes the most sense to draw from seawater or another saltwater source, desalination will probably be used to produce fresh water that’s safe for use.

βš—οΈ What Is A Desalination Plant?

A desalination plant is a facility where large-scale seawater desalination takes place.

The facility is equipped to treat large volumes of salt water per day. It may be a private plant that provides desalinated water for a specific purpose (such as for a factory, farm, or commercial facility), or it might be owned by the local government and provides desalinated seawater to the community for a variety of uses.

Desalination plants may use one of several technologies to remove salt from water. We’ve shared these in more detail below.

An estimated 21,000 desalination plants now operate worldwide, with some of the biggest plants located in Israel, Saudi Arabia, and the United Arab Emirates. The World’s Largest Desalination Plant is located in Saudi Arabia.

Desalination is an expensive process, which is why we don’t extensively use desalination plants to treat sea water all over the world. In many cases, it’s cheaper to transport fresh water from another location than to carry out the desalination process on a large scale.

So, while desalination plants seem to be the answer in water-stressed communities, the costs and energy required for sea water desalination are so high that most communities would do better to focus on other means of accessing a water supply and conserving what fresh water they already have.

Desalination plant

πŸ”Ž How Does Desalination Work?

Desalination works by removing salts and minerals from water, which makes it safe for drinking or agricultural use.

Seawater is pumped into the plant, where it is treated by the plant’s desalination technologies before being pumped into a private or public water system, depending on its intended use.

There are a few different desalination methods that may be used at desalination plants. The most common of these are multi-flash distillation and reverse osmosis.


Distillation occurs when salt water is allowed to evaporate and condense on a cool surface, leaving the impurities behind in the evaporation location.

There are a few different types of distillation, including natural evaporation, solar distillation, multi-stage flash distillation, vacuum distillation, and wave-powered distillation.

The most popular type of distillation used for seawater desalination is multi-stage flash distillation.

A seawater desalination plant that uses multi-stage flash distillation sends water through a series of flash evaporations. With each flash process, the energy produced from the water vapor condensation in the previous step is used.

Reverse Osmosis

A reverse osmosis desalination plant uses reverse osmosis membranes to remove the majority of total dissolved solids from water, including dissolved salts and minerals.

RO is the leading desalination process today. Reverse osmosis filters send salt water at a high pressure through a semi-permeable membrane, which rejects salts and other contaminants. This high-pressure reject stream is flushed out of the system while the pure water molecules continue out of a different exit.

RO technology for seawater desalination continues to improve. New plants can use more efficient technologies, reduce their plant footprints, and lower the cost of their energy sources.

There are a few factors that affect the efficiency of RO, including:

  • The presence of calcium and magnesium
  • Colloids and other insoluble impurities
  • Viruses and bacteria
  • Dissolved organic carbon

Water must be processed in a pre-treatment stage, which may add anti-scaling agents, fouling inhibitors, and organic polymers to the water, to prevent damage and fouling of the membrane. The semipermeable membranes should also be cleaned routinely and flushed with fresh water.

There are a few other types of osmosis that might be used at a seawater desalination plant, including forward osmosis. However, reverse osmosis is the most popular method.

Reverse osmosis desalination plant
James Grellier, CC BY-SA 3.0, via Wikimedia Commons

πŸ“€ At-Home Water Desalination

Reverse osmosis and distillation can also be used on a much smaller scale for at-home water desalination.

There aren’t many reasons why you should primarily want to remove salt from your fresh drinking water at home, since it should have very low salt concentrations anyway.

However, you might prefer to drink water that’s free from minerals, salts, and other dissolved solids – and reverse osmosis and water distillers can both provide this outcome.

You might also want a solution for removing salt from softened water, since water softeners add extra salt to water during the softening process.

πŸ‘¨β€πŸ”§ You can buy RO systems and water distillers for point-of-use water treatment, meaning that they’re installed near your kitchen faucet and provide fresh water on tap.

πŸ‘¨β€πŸ”§ There are also some reverse osmosis systems available for point-of-entry installation, providing salt-free water around your whole home.

Reverse osmosis system and distiller

βš–οΈ Pros & Cons Of Drinking Water Desalination

Now we know more about desalination and how it works, let’s look at the pros and cons of seawater desalination plants.

Pros Of Desalination

Accessible Drinking Water

In regions where fresh water is scarce but seawater is abundant, seawater desalination offers a simple solution.

Saudi Arabia gets almost 70% of its fresh water from desalinated seawater, and many Caribbean Islands rely on desalination plants for access to safe drinking water. Regions that are prone to drought may also use seawater desalination as a backup method of drinking water production.

Reliable Process

The distillation and reverse osmosis processes used for seawater desalination are highly reliable, meaning that they’re guaranteed to provide high-quality water consistently.

It’s reassuring to know that we can use this method of water treatment in the future if a fresh water crisis occurs, especially since the ocean is such a vast water source that would provide an almost inexhaustible supply.

Protects Freshwater Supplies

Regions that use desalinated seawater for some or all of their drinking or agriculture purposes can better protect and conserve freshwater supplies.

This provides environmental benefits and conserves habitats in freshwater sources.

Cons Of Desalination

Expensive To Build And Operate

One of the biggest disadvantages of a seawater desalination plant is the costs associated with building and operating the plant.

It costs millions of dollars to build even a small plant, and a huge amount of energy is required to keep the plant in operation. Changes in energy prices have a big impact on the plant running costs.

Bad For The Environment

While seawater desalination can help protect and conserve fresh water sources, it also has a negative environmental impact due to its high energy usage and its salt disposal methods.

A desalination plant dumps the discharge from desalination processes back into the ocean or injects it underground. The high levels of salt in this brine solution may be damaging to marine habitats if the discharging method isn’t carefully monitored and regulated.

Toxic brine from water desalination plant released into ocean

Might Contaminate Water Supplies

Generally, a seawater desalination plant should produce high-quality, pure water. However, there are certain chemicals that may be used in the desalination process that could affect the quality of the end result.

The exact chemical and biological contaminants added to desalinated seawater depend on the plant’s location, technologies, and design.

πŸ“‘ Final Word

Seawater desalination is a reliable, effective method of water treatment that’s increasing in popularity, especially for agricultural use.

However, this method of water treatment has a few major downfalls that will likely prevent it from ever being used as a primary method of producing pure water – unless the world experiences a fresh water crisis.

❔ Seawater Desalination FAQs

Is desalinated water safe to drink?

Yes, desalinated water is safe to drink – as long as the water has been treated for drinking purposes and has had additional filtration and disinfection (if needed) to remove harmful contaminants and microorganisms. Most water desalination methods also remove dissolved solids as well as salt, which makes the water safe for human consumption.

Can you use desalination to remove salt from softened water?

Yes, you can use a desalination method at home to remove salt from softened drinking water. We recommend using a reverse osmosis filtration system for this purpose.

Is desalinated water healthier?

Desalinated water is healthier than drinking high-salt seawater, which is dangerous to drink and would quickly dehydrate you, potentially leading to death. However, desalinated water isn’t healthier than normal tap water because it’s lacking a number of essential trace elements that are found in fresh water supplies, including magnesium, calcium, and iodine. You can get these minerals from your diet, but it’s still good to consume them in your drinking water.

Where does salt go after desalination?

The salt from a seawater desalination plant is drained along with wastewater and is injected underground or dumped in the ocean. In some cases, the salty water might be spread over the land. However, recent research from MIT suggests that this waste material could be converted into useful chemicals, including sodium hydroxide, which could then be reused for pre-treatment at the desalination plant.

What’s the biggest problem with desalination?

The biggest problem with desalination is that it costs a lot of money and uses a lot of energy. Large-scale desalination processes are energy-intensive and increase greenhouse gas emissions and fossil fuel dependence. These processes are much more expensive than other water treatment methods, which is why they’re rarely favored as a method of drinking water treatment.

Why can’t we desalinate ocean water?

We can physically desalinate ocean water, but the reason why we don’t use seawater desalination to produce filtered seawater for drinking is that it has high energy consumption and costs a lot of money. There’s also the environmental impact of producing reject water at desalination plants, which is often pumped back into the sea.

  • Laura Shallcross
    Senior Editor

    Laura is a passionate residential water treatment journalist who holds an undergraduate degree in Print Journalism and a master’s degree in Creative Writing. Over a span of 5 years she's written on a range of topics including water softening, well water treatment, and purification processes.

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