You won't find botulinum in creek or lake water. Just bring it to a boil and you'll kill everything in it. They used to say to boil it for 10 min or something like that. Nonsense. The bugs start dying at about 160 and by the time it boils, they're all dead. You don't even have to get it to a boil but most hikers don't have a thermometer with them so bringing it to a boil is an easy way to do it.
