Eli5: why haven’t we started considering or implementing large scale desalinization in response to our water shortages?
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Large scale desalinization is in use today although the definition of “large scale” is pretty important. While people discuss water shortages as a global issue, the crisis areas are local. Large scale desalinization in one location cannot solve the problem of water shortages hundreds of miles away.
Desalinization requires several things
1) Local source of salt water. This pretty much rules out this solution for any inland area. Water is HEAVY. Transporting it takes lots of energy and infrastructure.
2) Large amounts of available energy. Here you have to consider costs and alternative usage. In a poor and energy starved location, energy would either be too expensive or have many alternative uses of greater benefit.
3) A relatively concentrated population that would benefit from it (locally!). This makes desalinization useful in places like Singapore, Israel or Saudi Arabia in cities. It won’t be useful for sparse populations spread out across large areas.
To the matter of scale, desalinization cannot (at this time) be a solution for anything other than human use. Humans might use up to several tens to several hundred gallons a day per person. Wide scale agriculture, on the other hand, uses water by the acre-feet – ie hundreds to thousands of times more water than cities, by and large. And the productivity (economic output) of cities is FAR higher than agriculture or livestock farming.
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