We get fresh water from seawater through a process called desalination. This involves removing salt and other minerals from seawater to make it suitable for drinking and other uses.
Desalination Methods:
There are several ways to desalinate seawater, including:
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Distillation: This traditional method involves boiling seawater. The water vapor is collected and condensed back into liquid, leaving the salt behind. As mentioned in a Reddit AskScience post (https://www.reddit.com/r/askscience/comments/axqtel/why_dont_we_just_boil_seawater_to_get_freshwater/), this is a historically significant desalination technique. A simple setup might involve a pot with a lid and a collecting cup, as described on wikiHow (https://www.wikihow.com/Turn-Salt-Water-Into-Drinking-Water).
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Reverse Osmosis (RO): This is a widely used modern method. Seawater is forced under high pressure through a semi-permeable membrane that allows water molecules to pass but blocks salt and other impurities. Singapore, for example, uses RO in its desalination plants, consuming approximately 3.5 kWh/m³ of energy in the process ([Desalination is an energy-intensive water source]). The San Diego County Water Authority utilizes a large-scale RO plant in Carlsbad, processing 100 million gallons of seawater daily.
Both distillation and reverse osmosis are discussed in an article from the Washington Post (https://www.washingtonpost.com/climate-solutions/2021/09/28/desalination-saltwater-drought-water-crisis/). The Washington Post article and Iberdrola (https://www.iberdrola.com/innovation/desalination) both highlight desalination as a key method for obtaining freshwater from saltwater. The process, as noted by the USGS (https://www.usgs.gov/special-topics/water-science-school/science/desalination), is crucial for providing potable water. The byproduct of desalination can be used for various purposes as detailed in the Wikipedia article on desalination (https://en.wikipedia.org/wiki/Desalination).
Why can't we just drink seawater? As explained by Scuba.com (https://www.scuba.com/blog/how-to-purify-salt-water-an-essential-survival-tactic/), our kidneys cannot effectively remove the high concentration of salt in seawater, leading to dehydration.
