No no. Use an objective measure of water cleanliness, such as spread of cholera.
en.wikipedia.org/wiki/Cholera
Cholera is a proxy for dirty water and the link I provided shows that the outbreaks are much less severe these days.
When I was a kid, we got our water from a spring. When I was maybe five or six, the whole family contracted Hepatitis A; doubtless from point-source pollution.
Those springs are a lot cleaner now, and I drink freely from them and never have any ill effect from doing it. Of course, I guess I’m now immune to Hep A.

But I never hear of anybody else contracting it either. When I was a kid, people plowed hill land and raised animals on practically bare dirt and had outdoor privies. People thought cattle had to be afforded shelter in barns, when the climate didn’t actually require it, creating horrible quagmires of dirt, hay and manure. When it rained, the water ran everywhere from all those places. Now, the land is covered with forest or thick, thick sod-forming grass upon which cattle are rapidly rotated and through which water must filter so slowly and through so many organic processes that most of it sinks, highly oxygenated and pretty clean, into the further-filtering limestone karst formations instead of blasting downhill into every low spot, which included springs and wells. Nobody plows the land anymore because people have come to realize the topography is just too steep for it. But being in the “fescue belt” the “bermuda belt” and “bluestem belt” all three, it is highly productive even so. More so than it ever was before. But people didn’t know any of that then. People fought soil-holding Bermuda, Bluestem and crabgrass back then like they were the Pharoah’s Curse, when they’re actually good things.
The springs and creeks also flow discernably more water now than they did years ago, with fewer and less dramatic ups and downs.
People simply learned how to do things better. Nothing mysterious about it.