The problem with all the articles is they only address Giardia.

Generally I go upstream from trails to get water, but no matter how far I go, there could be a dead animal in the water around the next bend. Or there could be drainage from an area where a lot of animals poop.

The one constant I've seen since the 60's has been to purify water. We never actually did it in the 60's, but there weren't as many people around then.

In the 70's I started hearing about Giardia in Colorado. It has been a constant since then unlike a lot of the other scares that have come and gone. I don't know if Giardia even exists or if it has a big chance of making me sick. But I figure if I drink enough water from streams, I'll probably run across something that would eventually make me sick. Filtering is such an easy precaution to take.

Even if there were no germs in the water, there are many times I use the filter to get water I wouldn't otherwise be able to get. Such as hollows in a rock after rain. So it's not like I'm carrying any extra weight.

I put it in the category of wearing a motorcycle helmet. The chances of one ever protecting me from injury are very slim. Problem is, I don't know which time on the bike I'll need one.