We have just recently purchased a water filter, the name escapes me right now though.
It has an Iodine filter, and then a carbon filter after that. The purpose is that the iodine will filtre out bacteria, viruses, protoza etc, and the carbon will filter out the iodine and the silt. (I think, or very close to this, the sales guy told me ALL about it, and it sounded very safe.)

We paid $99.99 for it. I have not had to carry water to a camp site, or on a hike for a month, and its a huge huge huge difference. We each bring 1 empty 1.5L bottle, usually drink them in the car on the way there, then use the empties. We fill our bottles whenever we need to, and we needn't carry tonnes of extra water weight.