How can urban populations affect a water supply

They mostly affect it negatively. Often times, urban populations can overcrowd, overuse or pollute a water supply. Take the river Thames for example, in London. It's used so much that its waters are hardly safe to swim in, much less drink. Also, we cram water in reservoirs, making it safe for us, but keeping local wildlife from it.

Have a great night/day!

-Dylan (AKA Animus