And a lot of people got sick and died
You are being quite overdramatic.
Humans were drinking surface water for a long, long, long time.
Way before Berkey water filters were invented!
And actually, much of North America has a limestone/shale geology which is about as perfect a filtration/decontamination system as naturally exists.
Bad water kills whereever people are even today. Any ground water has the potential of being contaminated. Well water is usually safe because its been filtered.
Yes sand and earth will act as filters. To discount the dangers of bad water is just ignorant.