> My thinking is that treating water at home is not that hard. You can easily have one filtered tap at home. It's cheap and easy to retrofit.

I mean, define 'filtered'. A brita-type filter will do precisely nothing for most things that require a boil notice (nor will it do anything for most heavy metal contaminants etc).

In general, "filtered" taps primarily remove chlorine and calcium carbonate, mostly for taste reasons.

Doing actual water treatment at home is not going to be particularly economic or safe.