>>38376 >constructed wetlands FTW >you can turn dessert into oasis >and most of the water is the runoff to rivers/oceans anyway, it is lost if not captured
It can be dangerous if done wrongly. Active irrigation ruined part of Central Asia near Aral "sea". Agriculture used water from two local rivers, Amudarya and Syrdarya for extensive irrigation (mostly for cotton), and first it was good, but then sea gone and desert with salt and fertilizer remains formed. Sand storms take that dust and do damage to crops, even at hundreds of km. It also damaging for wildlife and locals.
Wrong usage of water, especially on sand soils, also may result in washing out fertile component, so after some time soil also becomes pretty poor.
So, extensive human-made usage of water is pretty complex concept that requires good scientific practice and skills. Stalin also had idea to turn Siberian rivers southward to add additional water to Central Asia, but project didn't happen.