Obviously this is region specific, but slowing down water is one of the best ways to have fresh water.

Slow it down from trickling down a slope and you have two things: more vegetation (which also retains water) and more time for that water to penetrate the ground for local wells.

You can completely "terraform" a desertic region https://youtube.com/shorts/cfhbtgon4Nk?is=oAExB5UeMAsShBux