Tso firstly the people who claim to care about the environment are against development. They don't want new wind farms, they don't want new hydroelectric and they certainly don't want new nuclear. They are OK with solar but only if you put it where you already are, they don't want desert wastelands to be covered in solar, I have no idea why.
So the ideologs who you would think would be for this are against it because they are retarded ideologs. The other group, the capitalists will do it if they think they can make a return on the investment. There are some areas where it is happening.
The issue is most of our water is used for watering plants. Shitty ass lawns and food for cows and the like but also crops like almonds need lots of water. Us humans like living in areas where plants grow well, so we kick the farms off the best land and plant suburbs there instead.
Lastly why bother, we have ample fresh water, the Mississippi discharges 90,000 gallons per second and the great lakes are fucking overflowing. We just need to pipe it around, which is actually cheaper and more environmentally friendly than pumping water through bazillions of tons of plastic xenoestrogen reverse osmosis filters. But the great lakes people are dicks and throw a hissy fit any time someone threatens to steal a drop of their water, while at the same time bitching about the rising levels washing away their homes.
In short, we're fucked because humans are not inelegant life forms.