I’ve been a big outdoors person all my life and regularly go backpacking and drink mountain stream and spring water. I’m also a big advocate of being realistic

I’ve been a big outdoors person all my life and regularly go backpacking and drink mountain stream and spring water. I’m also a big advocate of being realistic about risks and not sweating stuff that’s scary but extremely unlikely. That said, I know people personally who have had giardiasis. It’s awful. On a typical backpacking trip I’ll get water from from a bunch of different sources along the way, often not knowing what’s upstream. A few seconds of stirring my water with a lightweight UV sterilizer pen which I bought for $60 years ago is relatively low cost insurance against a risk which is hard to assess in the moment. My understanding is that much of the research on giardia et al has been in a few specific wilderness areas, and widespread sampling studies of many water sources are fairly few, so using what little research does exist to inform my decision to drink directly from a random mountain stream seems dubious.