I don't think they're uneconomical. Fresh, clean water is astonishingly cheap; of course people are using it to grow almonds and alfalfa in the desert.
Just charge people what the water is worth and they'll stop, or water companies will be able to afford much more treatment capacity.
You have a point about sequestering CO2 molecules, but:
a) I'm sure this will get cheaper over time, just like every other technology
b) we should be using solar and nuclear for everything
> Fresh, clean water is astonishingly cheap
Because you can find it in "concentrated" form (think entropy), all in an aquifer or a river, and these are everywhere. But these dry up because of our usage and the climate, and when they do you still have the same amount of water on the planet, it's just not as easily accessible. It's super spread out, it's too far away, it needs a lot of expensive processing to make usable, or all of the above.
What's cheaper and easier for you, to condense a cup of water from the air or to just turn on the faucet?
> we should be using solar and nuclear for everything
Why solar? Energy is not lost/consumed in the universe, so why not collect it from anywhere else. Energy is astonishingly cheap, that's why we use so much of it. If you know what I mean...
Energy is never lost, however, it’s transduced into less and less useful forms due to entropy.
People grow almonds in the desert specifically because they have access to artificially cheap water. In the U.S. lots of land comes with water rights: e.g. if a river or creek passes through your land you can use x% of the water to irregate your crops. Some of these water rights date back to the 1800s and they're locked in.
The water rights can be clawed back a couple ways: if they're unused for X years, or in times of drought.
There's an exception for droughts though: farmers with trees (that would die if unwatered) still get priority, while people that grow crops that replenish each season (like wheat) don't.
So this leads to perverse incentives where these farmers need to find a way to use ALL of their water, every year, or they'll lose access to their absurd water rights from the 1800s, and they need to use it on trees so it doesn't get clawed back during a multi year drought.
So, they end up planting the most water-hungry trees they can grow on their land (almonds), then they get to sell them to the world at artificially low prices because the water that was used to grow them is almost free.