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