I now live in Davao City, a city of 2+ million people, with one of the best water systems in this country, and maybe the world. I pay $10-12 a month for safe, treated water from the mountains. I drink it. I have had NO problems or systemic reactions. It does have that telltale taste of "city water".
For those who cannot pay for that source, there are lots of rain gutters feeding plastic drums. They scoop the water, and use it for flushing toilets and bathing. They also use it for cooking. Most will buy bottled "spring" or "purified" water for drinking, but also many just use the local San Miguel beer for their drink of choice (although coconut wine or "tuba" is also relatively cheap and gives them a great buzz!).
It makes me wonder how the people of Detroit will fare when the food stamps run out (not really! I already know the results!!!).