Can You Make Seawater Drinkable?

By Rehan Iqbal

It’s common knowledge that seawater is not safe to drink. Not to mention, totally unpalatable. In a world that is changing rapidly, there are concerns about increased droughts. In fact, in some areas, this is already a harsh reality. Given the urgent need to secure fresh water, an important question needs to be answered: can you make seawater drinkable?

woman sitting on yoga mat with water bottle

This article is going to fully answer this question. There are several methods of desalination. This is the process of removing dissolved salts from water. Large-scale seawater desalination plants have existed for quite a while, but these tend to be more expensive than more common sources of freshwater.

Despite the cost, in some areas desalination is the best method of providing safe drinking water.

Why is Seawater Not Fit for Drinking?

Because of the high concentration of salt, sweater is toxic to humans and animals not adapted to living in the sea. Normally, our kidneys remove excess salt and flush it from the body as urine. In order to do this, we need fresh water the remove the salts.

Because seawater contains high levels of salt, it is impossible for our bodies to use this same water to remove the salt.

How to Remove Salt From Seawater

Salt is removed from seawater in a process known as desalination. This is also used to remove salts from brackish ground water. The two most common ways of making seawater drinkable is distillation and reverse osmosis.

Distillation

Ancient Greek sailors discovered that using the sun to evaporate sea water and then allowing it to cool and condense, removed the salt. Distillation provided safe water for drinking when out at sea for prolonged periods. This is the first known use of distillation to make seawater drinkable.

Using a plastic bottle, with bottom cut open, and soda can placed inside, is a modern equivalent to the water distillers used in ancient times.

Sea water is placed in a soda can that has been cut open. The plastic bottle has a hole in the base, just large enough for the can to fit into. The bottle forms a sealed dome that fits over the can. As the water evaporates, it collects along the inside of the bottle and condenses. Distilled water trickles down the side of the bottle and collects in the bottom as clean drinking water.

Water distillation is now common, both for commercial use and at home. A countertop water distiller is relatively cheap and easy to obtain. These devices work in the same way as large commercial water distillers, just on a smaller scale. You can distill water at home with very little cost involved.

How Does a Water Distiller Work?

A water distiller heats the water electrically until it boils. The evaporated water (steam) collects in a condensation chamber where it cools and reverts back to being liquid water.

Salts, most other minerals, and other contaminants don’t evaporate at the same temperature as water. This means that the salt (and other contaminants) are not present in the water vapor when it condenses back into water.

Distilled water is almost 100% pure and safe to drink. Though, because just about all the minerals have been removed, distilled water has a bland taste.

Reverse Osmosis

In some coastal cities, with a limited natural fresh water, large commercial reverse osmosis (RO) water filters are used for the municipal water supply. Industrial RO water filtration plants can supply enough water for any size city. The construction and maintenance of these facilities are costly.

RO water filters for the home are also very popular. This is generally accepted as the best type of water filtration system. RO water filters are not only used for desalination. They are capable of removing over 90% of all contaminants found in any type of water supply.

How Does Reverse Osmosis Work?

Osmosis is a natural phenomenon. It is a process whereby molecules move from a point of high concentrations to that of a lower concentration when passed through a semipermeable membrane. An equilibrium is obtained, whereby the concentration of molecules are equal on either side of the membrane.

Reverse osmosis uses pressure to reverse this process. When pressurized water is passed through an RO membrane, solids (like salt) are trapped in the membrane. This removes around 95% to 99% of dissolved salts from the water.

When desalinating sea water, using reverse osmosis, a pump is used to pressurize the water. This added energy is what allows the RO principle to work. A home RO filtration system does not usually require a pump, as the municipal water pressure is sufficient to cause the desired reaction. In some instances, where water pressure to the home is not adequate, a small electric pump is used to increase the water pressure.

Water passed through the RO filter is collected in a storage tank to be used on demand. The salts and other contaminants are flushed away to a drain. RO water filters often use a lot of extra water (increasing water consumption) as a result.

Home RO water filtration systems usually have many stages besides the RO membrane. A prefilter is commonly used to remove larger particles from the water before it passes through the RO membrane. This prevents the membrane from becoming blocked, thereby prolonging the lifespan of the RO filter.

Activated carbon and other filtration media can be used to remove additional chemicals and toxins in the water. This removes bad odors and elements that may discolor the water. Additional stages may alter PH of the water, remove harmful minerals, and kill bacteria.

Advanced RO water filters can utilize more than 10-stages of filtration, ionization, demineralization, and remineralization – replacing essential minerals that may have been removed during the filtration process. Silver and UV lights are often used to ensure that the water is free of bacteria and viruses.

Depending on the quality of the water supply, any combination of filtration stages can be used to ensure perfect water quality for drinking, cleaning, and plants.

Less Common Methods to Make Sea Water Drinkable

There are other methods of desalination which are less popular because of the cost involved or the complexity of the system.

Electrodialysis: Uses an electric current to ionize salts that are passed through a membrane.
Vacuum Freezing: This principle is commonly used to preserve perishables, like coffee and some food products. In a vacuum, the boiling and freezing temperatures are altered. By freezing water in a vacuum, solids (like salts) do not freeze at the same temperature. This allows dissolved salts to be separated from the water in a similar way to distillation.