Fortunately humanity is relatively tolerant to water quality. We probably are tolerant because for at least a million years there was no water treatment and in some measure have adapted. Certainly a significant part of the population lives with no water treatment. It's interesting to me that one of the recent improvements in water quality in parts of Africa is to simply fill a former clear plastic water bottle with water and leave it in Sunlight for a couple of days.
During our spring 2008 trip across Labrador a number of communities had drinking water warnings. When we asked the locals about it they simply said they ignored it with no ill effects.
For us when driving thru suspicious areas we filter our water on the 'way in' and if really concerned have filtered it on the 'way out' at the tap. For tap filtering we have used a super filter that really removes virtually everything except the water.
Trav-L-Pure Camper Canister - Water Purifiers and Water Micro Filters - General Ecology
I've always wondered about 'way in' filtering because it can remove protective chlorine.
As our RV years have passed we have become less concerned about water quality but do carry a tap filter when we are entering an area of concern.
Probably if we gave our home water systems equal scrutiny we might show similar concern but in reality water quality is really near the bottom of our concerns in the USA and Canada.
Safe water and travels,