You've got it a bit backwards. Large swathes of human population do experience issues with water availability. However, richest parts of the world are where w

You've got it a bit backwards. Large swathes of human population do experience issues with water availability. However, richest parts of the world are where water was traditionally in abundance, and human settlements have been created around large bodies of (drinking) water. Confluences of rivers into (non-frozen) seas is the sweetspot: pottable water and cheap trade routes. So you come from a rich part of the world because it's got a great balance of natural resources, but humans are there because of it: it is no accident! Btw, canals (as in human built rivers) might have been part of the problem. They might also be part of the solution going forward.