Berkey systems are the gold standard for gravity water filters as shown in independent lab testing. The results of which you can review here.
Our Black Element filters not only filter water to the highest purity but they do so at the lowest cost of any alternative; roughly 2 cents per gallon. Compare that to brita filters (20 cents) and bottled water (120 cents). The black element filters can easily purify tap water, yet are powerful enough to purify raw, untreated water from lakes and streams. In the event of a natural disaster they can be essential in removing viruses, pathogenic bacteria, cysts, parasites, pesticides, herbicides, pharmaceuticals, heavy metals and impurities all below detectable levels.