We are still very much living in the land of the dinosaurs -- well, their urine, at least.
Dinosaurs were on Earth way before humans, and they spent a great deal of their time leaving their marks in the fresh water supply.
The water literally passed through them, leaving molecules for us to gobble up by the glass.
This brief but fascinating video also explains how Earth's freshwater reservoirs work. Basically, they provide water to land animals well before it reaches us.