[pixl97]

>That's because it comes from a lake high in the hills above any industrial or agricultural activity.

Half correct, but not completely correct..

I'm also assuming it remains very cold or even frozen for a huge portion of the year. The water is never getting to a temperature that allows much of the dangerous things to humans to grow. For example here in Texas you're apt to get amoebas in the 25-35C waters.

Also that high in the mountains you're probably getting water off mineral rock that's had very few interactions with the biosphere to accumulate wastes from animals.

You don't need industrial or agricultural activity to kill you.