I've wandered the Scottish Highlands for many years camping and using bothies never filtered water - mind you I mostly consume coffee or tea so maybe the small amount of boiling killed off any beasties. Mind you - I am fairly careful about where I get the water (check for any dead animals upstream, don't take water from anywhere that is obviously frequented by animals or people).
Meanwhile, my wife got a nasty case of cryptosporidium - GP suspected it was from a swimming pool!
Meanwhile, my wife got a nasty case of cryptosporidium - GP suspected it was from a swimming pool!