Why can’t we just pipe in saltwater to areas low on water and remove the salt for watering plants, etc?
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Pretty simple answer that Google could’ve told you. Desalination requires a large amount of energy.
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Couple reasons, taking the salt out of water is very energy intensive. It can be done through reverse osmosis which essentially means pushing the salt water through a very very fine filter so that only the water goes through, and the salt is unable to transfer through to the side of the filter without salt. This needs a lot of pressure, so the energy cost is high.
Also there would be a lot of build up of salt within the pipes and corrosion of the pipes from the salt water being moved. It would need a lot of maintenance and repairs.
It is possible to remove salt from water, it is called desalination. The problem is cost in building the facilities and removing the salt from the water.
The cost is around $0.50 per cubic meter, which might not sound like a lot until you look at the water required to produce food. You need around 1500 liter =1.5 cubic meters of water to make 1kg of wheat and need around 15,000 liters for beef. So growing a kilogram of wheat require around $0.75 of water and $7.50 for a kg of beef. That is a quite significant cost increase.
Water is also heavy and you need a lot of energy to lift it up. We use the potential energy from elevation in hydroelectric power plants So pump it up to a location where there is not a lot of water cost a lot of additional money to power the pumps.
So it is something that technically can be done, the problem is one of cost and a way to get the required energy.
Desalination makes sense economically for human domestic usage not for agriculture.
Desalination of water takes a lot of energy and creates super salty brine as a byproduct. Most of the time, it isn’t worth it. Even if the energy cost is worth it (California and Saudi Arabia are the only locations I can think of pioneering the technology).
The brine is also hard to dispose of. You can’t just dump it in the ocean or on the ground without destroying the local ecosystem. You also can’t sell the salts because salt is one of the cheapest resources on Earth. You wouldn’t be able to give it away fast enough with the amount of water we use.
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