If you have seen this Vid or one like it it's Not true.

There is almost no running water that is safe to drink,at one time it was true.Even if there are no factorys,etc there is still run off from farming poison rain etc.

I suppose if its drink it or die now vs drink and get sick or die later,I probally would drink.But if you prep you will have a filter and or treatment in your kit and you will not die from water or lack of,preferablly you will die from old age after long healthy life well hydrated.