eli5: Why is it so difficult to desalinate sea water to solve water issues?
In: 1972
Salt really likes to dissolve in water and stay there. It’s hard to get it out, and what that means in practice is that it takes a lot of energy to do it. Which means it’s both expensive to run/build, and potentially environmentally problematic depending on your energy source.
Anyways, there’s two primary ways that it’s typically done. You can heat up the water until it evaporates. The water turns to vapor and floats away, leaving the salt behind. Then you can collect that vapor and condense it back to liquid, and you get nice fresh water. But it takes a lot of energy to evaporate a significant amount of water, especially if you want to do it in a relatively small footprint (Sunlight evaporates millions of tons of water every day, but there’s no easy way to collect most of it).
The second way is to force the water through filters that are designed to separate the salt from the water. The problem with this is that to do it at a meaningful scale, you need a lot of filters (which require fairly consistent maintenance/replacements) so operating costs are high, and you generally need to pump the water through those filters at high pressures, which means more energy use, and more costs and so on.
Unfortunately, neither of those methods get particularly great economies of scale as you size up the operations, so it’s generally just rather expensive.
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