Bacteria are living creatures just like us. Deprived of food, water, shelter from harsh environmental conditions they die.

Most municipal water supplies are chlorinated and they work hard to make sure that water that leaves the plant has enough residual chlorine to fight off incidental contamination from human hands and infiltration from loss of pressure.

In one well publicized case in the 80s a DIY plumber working on sewer line tied into a water line and created a situation where a small but steady amount of raw sewage was pumped into the water main. This went on for some time. After a time local plumbers started getting calls from homeowners complaining of reduced water form from their shower heads and faucets. The plumbers find the aerators and shower heads clogged with little black and white specks. They clean them out and flow is restored. But after a few days the problem returns.

After a time people start asking questions about what the material is and where it is coming from. They ask the water plant operators. They sample the water coming from the plant and find no specks. They take a sample to a state lab and testing comes back that he sample is black bits are composed of undifferentiated complex organic material and nitrogen compounds, and the white stuff is cellulose. In non-lab speak - feces and toilet paper.

There was, needless to say, an outraged reaction.

The sewage was tracked back to the botched plumbing job and the situation corrected.

The good news was that nobody got sick. At least not beyond the psychological effect. The system worked. The residual chlorine in thousands of gallons of treated water effectively killed the bacteria from a few score gallons of raw sewage. The people living at the house where the sewage-to-water connection was made were most at risk. Because they were drawing their drinking water from the location where the sewage was most concentrated, and where the chlorine had had the least amount of time to do its job.

Before anyone gives up on municipal water and shifts entirely to bottled water for drinking you have to understand that municipal water supplies are tightly regulated. Bottled water is much less well regulated and tested.