Yes. Always, somehow.

Depends on the source, but typically if I am unsure.

Always. When backpacking, I have used filters or iodine or boiling. In my BOB, I have means to do any or all as needed.

That said, if I have none of these available and I am lost in the wilderness I'm drinking the water I can find unless I know it to be bad, especially if I expect rescue within 3-4 days. It takes days for most water-borne diseases to show up. I could be dead of dehydration before that if I drink nothing at all...

Always - either carried in from home, boil or filter. Always

Given the choice, chemically purified, filtered or boiled. Or all of the above. I've seen a dead beaver floating in a pond the morning after drinking water I'd taken from it. Glad I'd boiled that stuff. ICK!

I think a lot of this is from the ultralighters. I was glancing a book on lightening your trail hiking gear and they suggested it wasn't really needed, after all the author had been hiking for years without it and had never had a problem. *shudders*

I always filter water when I'm out in the woods, whether I'm camping, hiking or practicing primitive skills and whether or not I'm familiar with the water source.

We have a Royal Berkey filter, and all our drink and cooking water goes through that. I haven't had to deal with outside water lately, as we haven't gone camping in almost 5 years now (sigh).

I would never, ever, ever, drink uncleaned water again... (At least, that's my plan.)

I won't say every drop I drink gets filtered, but most of it goes through one before I drink it, even at home. When not at home, I'll confess to contribute to the amount of plastic in this world, it's easy safe and convenient.

I always either filter or boil water I find in the wild. This is a habit I developed after unfortunate experiences drinking untreated water in the Colorado Rockies. Any water I use for washing, drinking, cooking, etc. gets treated.

Yep, I agree, I filter my tap water just for palatability, and have the MSR and the Steri pen for worst case scenarios. I also treat my stored water (which is tap water run through an RV style filter).
Better safe than sorry. You never know, why not take the extra precaution whenever possible.