The responses on this thread are really kind of funny
Just for fun, try wikipedia with the topics "Roman aqueducts" and "Drinking water"
From the second... Although most fresh water sources are drinkable by humans, they can be a disease vector or cause long-term health problems if they do not meet certain water quality guidelines.
So if you are going to drink from the same source extensively, consider the second part of that sentence.
BTW. About 12% of the household wells in NJ are failing the water standards tests for various reasons.
Oh no! I used to drink well water when I was a kid, but not in NJ. And still drink it from streams.
So if you are going to be at a single location (water source) for a few days, boil the water and save it when you are cooking.
If your sources are not going to be clear, filters will really help. (Like AT in NJ, e.g). That pond with algae probably has a lot of stuff growing in it that won't hurt you, and other stuff that your body will get rid of with some temporary discomfort. And maybe some nasty stuff that is really awful that filtering and boiling won't do jack for.
Your common sense will help, but as a consumer, you have probably already bought into extreme safety and had your common sense threshold altered. The nice thing about that is you can simply avoid thinking and buy American.