Even developed countries from time to time have difficulty delivering safe drinking water to some customers. Here in the DR it is a function of risk mitigation. I have placed my faith in a single bottled water supplier and maintain a stock of 20 or so bottles all the time. We use that for everything that results in consumption - cooking, drinking, brushing our teeth, ice maker etc. We have an under the counter osmosis setup for the dog's drinking water, washing dishes, wiping down kitchen counters etc.
I chlorinate the water in our cistern - it sits for a long time and gets quite warm in the summer months.
Most healthy people will eventually ingest some bacteria or protozoa but the body can usually combat those without major symptoms. I have more faith in the main bottling companies than I do in the water utilities, and in particular their distribution piping. Water from the main purification plants may be fine most of the time, but we all know the delivery pipes are broken and have leaks all over the place - each crack being a possible place of contamination.
So far our system has worked for us and bottled water is ridiculously cheap so I see no pressing reason to change. Using bottles is much more convenient when you have lots of them and get home delivery direct from the company.