For the US in particular, water issues come down overwhelmingly to unfettered agricultural use, often with crops like alfalfa that are both mostly water by weight and are shipped out of the country to other places. Domestic use is only a fraction of the total.

I am pretty sure that this is true in all developed countries. When you see farming without irrigation, you will see more poverty. It is very important for human development. That said, it could sometimes be done more efficiently, but more costly.