Berkey PF-2 water filters reduce fluoride and arsenic from water using aluminum oxide (activated alumina). What is important to know is that pure aluminum and aluminum oxide have very different characteristics. Pure aluminum is water soluble, highly reactive and has adverse health effects. On the other hand, aluminum oxide is not soluble in water, is inert, very stable and has no adverse health effects. It should also be noted that aluminum oxide is not treated with cyanuric acid. Learn more about aluminum oxide.