We drink our tank water too, but unfiltered/untreated.
Regarding rainwater (which we catch and use on the boat too) - when we were kids
had a holiday home at a beach and all water was rainwater - collected off the roof even though the seagulls seemed to like perching on there too. Didn't seem to do us any harm.
Whole communities pretty much exist only on domestic dwellings own tank stored rainwater and as far as I know untreated - for example, Bermuda
but there they do seem to keep their roofs nice and clean with fresh white paint