Filtration system in time of emergency

I want to purchase a ceramic candle (or similar) filtration system that I can use in time of emergency. I do not want something that hooks up to a current plumbing system. I want something that I can use with river water, for example, and turn it into drinking water. What do you recommend.

 For personal use, consider the Personal Emergency Gravity (drip) Water Filter   http://doultonusa.com/doulton_water_filters/Emergency-gravity-filter.php. For household/family use, consider  the GSS2 http://doultonusa.com/HTML%20pages/portable_systems.htm.
 These systems will all provide you with premium quality water from any water source (except for sea water). The only main differences is the container size, as well as, the total output (per hour, per day, total capacity).