Why don't we just boil seawater to get freshwater? I've wondered about this for years.

Olivia Thompson Olivia Thompson Sep 19, 2021 · 2 mins read
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As our population grows and our freshwater sources become scarce, it’s natural to wonder if we can simply turn to another seemingly endless source of water- the ocean. After all, seawater makes up 97% of the Earth’s water, so why can’t we just boil it to get freshwater?

Unfortunately, the answer is not as simple as one might hope. While it is technically possible to boil seawater and collect the resulting water vapor, the process is extremely energy-intensive and not economically feasible on a large scale.

To understand why, we need to dive into some chemistry. Seawater contains not only salt but also a variety of other dissolved minerals and impurities, such as magnesium, calcium, and sulfate. When we heat the water to boiling, the salt and minerals are left behind while the pure water vapor rises.

However, the amount of heat energy required to boil seawater is much greater than what is needed to boil freshwater. This is because seawater contains more dissolved solids, or “total dissolved solids” (TDS), than freshwater. The TDS in seawater raise the boiling point of water, meaning it takes more energy to reach boiling temperature.

In fact, to boil seawater and obtain freshwater, the water must be heated until it reaches a temperature of around 100 degrees Celsius and then boiled for several hours to ensure that enough water is collected to make the process worthwhile. This requires an enormous amount of energy, far more than is currently available using existing technology.

Additionally, the process of boiling seawater causes damage to the equipment used to do so. The salt and other minerals in seawater corrode and degrade metal, including expensive machinery. This further adds to the cost of the process.

Given these challenges, it’s not surprising that seawater desalination using boiling methods is not commonly used as a source of freshwater. Instead, desalination processes that use membranes, which filter out salt and other impurities, or other more advanced technologies, such as reverse osmosis, are used to convert seawater into freshwater. While these processes are also energy-intensive, they are more efficient and do not require the same high temperatures as boiling seawater.

As our fresh water sources continue to become depleted, it’s important to explore all potential sources of water. While boiling seawater is technically possible, it remains an impractical solution due to the amount of energy required and the damage it causes to equipment. In the meantime, we must continue to innovate and invest in alternative processes that allow us to obtain freshwater in a sustainable and cost-effective manner.

Olivia Thompson
Written by Olivia Thompson
Making a difference, one step at a time.