First of all, normally you need to figure the risks. I figure that the primary risk is from Giardia lamblia, so I take precautions against it, and I do not go after any virus, bacteria, or whatever. Friends of mine have gotten sick from untreated water.
So, I use a simple gravity filter with one raw water 2L Platypus, the filter, and then one clean water 2L Platypus, with some extra tubes. Then, if any sort of troubles would develop that would ruin the filter process, I carry some chemicals as well, and that is normally some chlorine dioxide liquids.
The one clean water Platypus can also serve as my extra water tank along the trail to augment my Gatorade bottle of water.
I have some thin cord attached to the raw water Platypus so that the whole thing can be hung up on a tree branch while it works.