Brine, salt water, things that come out of Desalination plants are normally put back in the ocean at an environmental cost. Why cant the brine be pumped somewhere safe, or have the salt removed and put somewhere safe? Arent there plenty of places on land to put all of that salt? Why cant the brine be pumped into the desert to evaporate?
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Fun fact: Gulf Coast countries that heavily rely on desalination tend to primarily desalinate ground water, not sea water. – Reject brine is still fed back into the original source, but that unfortunately aggravates the issue further, because with no precipitation, ground water does not see enough dilution to not be salty.
Because of the global cycle of evaporation and precipitation, the only source of “real” fresh water is rainfall (or snow, hail, pick your precipitate). So temperate or tropical areas with a lot of precipitation have fresh water stores underground that are constantly fed by water trickling through the many layers of the Earth’s crust until it “pools” in those underground aquifers. Arid desert areas that don’t see a lot of fresh water coming in often have ground water that is quite salty. Oasis are where the occasional aquifer feeds a spring, but aquifers are more common in some areas (e.g. Saudi Arabia) than others (e.g. the UAE).
Because of this dynamic, evaporating reject brine on the surface doesn’t actually remove salt from the system, it just creates an entirely unpredictable reservoir of salt that might trickle back into the ground water at any point, while also removing more water (which would have been returned in the reject brine, but has now been evaporated to late turn into precipitation that will not actually happen in place, but condense somewhere else on the planet).
So you might be thinking “why not just take the salt OUT of the water entirely?” – well, the short answer is: it’s just too hard. Desalination is essentially a progressive filtering process, which is very hard to get perfect if you are missing the liquid phase. So the salt water can be concentrated down, but not really split into its components. And while there are small-scale desalination plants capable of full removal, they are currently not feasible or / and cost-effective at the scale needed.
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