Thanks Marjorie I wasn’t aware of that one.

What Dusty said. But also, people develop tolerance to what they normally drink; this includes giardia.

Getting giardiasis in a survival situation could be deadly. 2 weeks of painful abdominal cramping and diarrhea when you’re already in a shaky situation?

Also, it was common knowledge throughout Europe that water wasn’t safe to drink. For centuries, a weak ale was the drink of choice, then tea. Not because of its alcohol content, but because both were heated to pasteurization temperatures. They might not have known exactly why it worked (germ theory wasn’t commonly accepted until the 1880s), but they did know that ale didn’t make you sick while the water could.

At one time there was natural forests and grasslands and low human population. Nature kept everything in balance and the water was safe to drink. The same applies to some remote unsettled areas today.
Then came cities, factories, farming and reliance on chemicals. They destroyed the natural setting and produced so much waste that nature can no longer deal with it. This was done to produce things we don’t need to make some people richer and as status symbols for the masses. This destroys the land, water, air and living creatures and is called progress.
Now you know why they won’t tell you.