Here in the Virgin Islands, much of our personal water consumption comes via rainfall we capture from our roofs into our cisterns (big underground swimming pools). Even with that I still need to truck in water a few times a year when the rain hasn’t been sufficient.
My roof surface area to consumption ratio is such that this system works pretty well for me (big roof, small human). However with a farm the roof surface area to consumption ratio is flipped - big fields needing water and little to no roof (maybe a tool shed or garage). And you can’t increase roof surface area since that would block sun from the plants. Industrial uses also have a poor ratio. Dense usage of water in a limited size building.
If we've posited a desert based system, I'm going to guess it is closed loop with respect to water (which is to say the water never leaves the system as anything except perhaps evaporation during post processing.) So the initial water budget probably comes from the aquifer or is imported. Once the system is running an interesting question is how much water would it lose over time.
And while that is an interesting question, it doesn't change the situation that no farmland was harmed in the process. :-)
I found it mind boggling when I went to Colorado to visit family and saw fields being irrigated to produce hay. The inefficiency of this compared to harvesting hay from areas where there is enough natural rainfall to support the growth of grass seems like a really poor use of limited water resources.
Worldwide farming is a ratio of 2.33:1 vs all other water use, 81% is 4.26:1 Aka a significant difference.
US Farmers generally measure water use in acre fee, each of which is 325,851 gallons and many farms are using more than that per acre. It’s not difficult to find farms that use more than 1 billion gallons of water per year. By comparison the entire US fracking industry is onky using about 25 billion gallons per year.
Unlike cities, farmers go where the water is. I know some HNers think farmers are growing crops in deserts. But that's just laughable. They farm where there is water: rivers, lakes, flood planes, deltas, etc. It is the cities diverting the water from these places.
We can grow crops with far less water. Look at farms in Israel. The problem is that water prices don't account for externalities or sustainability, so in the short term farmers have little incentive to conserve.
It turns out there are a lot of places with humidity but little rainfall. Most of California being one but also places in the middle east. Believe it or not, there are high humidity deserts. There are several companies doing this not for farming but for drinking water. Like Zero Mass Water:
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