Most natural water on Earth is only drinkable after boiling it, and it has been like that for ages, so there really hasn’t been a time where it was always safe to drink rainwater. Cholera, plague, and other bacterial diseases were common in olden times and are vanishingly rare in areas with water treatment plants for a reason.

Granted, there is now a lot of other junk in our water that makes some areas worse, but there are also bodies of water that are now considered safe for the first time since we started testing water as well. We need to stop throwing garbage everywhere and we need to better control runoff water that can damage the water table. But it isn’t a clear case of “water was drinkable and now it isn’t, return to olden times because humans are the virus” like the meme suggests.