I don't use a filter. Aquamira or Pristing Chlorine dioxide treatment for me, lightweight and reliable.

Personally my odds with that from *experience* over 5 years or so is that

1) I've never been sick
2) The chlorine dioixide doesn't give the water an off flavour
3) when hiking with more than two people who have water filters the chance is almost 100% that before the end of the trip one of them is mooching treated water from me because their filter has broken.

I find filters unreliable, slow, and heavy.
_________________________
Any fool can be uncomfortable...
My 3 season gear list
Winter list.
Browse my pictures