Most of the water in the lakes probably would be ok without filtering, as long as its from a mountain beck, however I've been really ill in the past from unfiltered water, so now just filter it all just to be safe
Carbon filters remove chemicals which regular filter can't, but as long as you don't drink water from near farms, or any other source of contamination you should be ok,
Me and April even drank water from a ditch with a dead sheep and didn't get ill with the sawyer, and having the ability to back flush with the provided syringe, it cleans the filter and it will last a long time
We've had ours for about 2 years now, and use them every weekend
Don't let it freeze tho in winter