The water wasn't polluted then and there wasn't that much waste nor people. I got a good read from this.
We did survive without it. Plain and simple.
The main issue now is pollution and water waste on a mass-scale. Starting with the advent of the Industrial Revolution and then being further bolstered by the massive population increases we've subjected the Earth and our environment to over the last century. Not to mention pollution of all kinds including dumping industrial waste and/or raw sewage into our fresh water supplies.
