Your base of operations should have a clean source of safe water, IMO. We've got a small creek that we get water from at the cabin, which is where I'll be when shit gets weird.
Giardia, AKA Beaver Fever, is really bad stuff. My Dad caught that once and we all thought he was going to die... and he probably would have if he'd have been solo. It reduced a Mountain Man to a weak helpless kitten in short order for a week. The uncontrollable fever, vomiting and diarrhea is very dangerous.
Filters and such are great to have around, but if you don't have that, then get a jug of water. Let it sit and the sediments will settle after a few hours, then transfer the clear(er) water to another container (just dump out the murky stuff left at the bottom)... do that a couple of times, using a shirt or something to help filter, and then boil it. Once you've boiled it, it'll be safe. Might not taste the best, but safe.
Interdum feror cupidine partium magnarum Europae vincendarum