Product Description Berkey Water Systems is the leader in gravity-fed filtration systems and trusted choice of adventurers, preppers, off-grid homesteaders and families for over 20 years. Berkey Systems were originally designed for extreme use for emergency preparedness and off-grid activities, and are also now used every day in millions of homes around the world by discerning, health conscious consumers who have declared water independence. Berkey systems provide economical, long-lasting water filtration for just pennies a gallon. No electricity, tools, or plumbing required. Berkey gravity-fed water systems are available in 7 sizes and are ideal for use at home, camping, fishing, RVing, or during unexpected emergencies and disaster scenarios. Enjoy delicious, refreshing water for just pennies per gallon. From the Manufacturer The PF-2 is for use with Black Berkey Purifiers - If you use ceramic filters, you will need the PF-4 *** PF-2 reduction elements are designed for use in conjunction with Black Berkey water purification elements to adsorb the following unwanted elements found in drinking water. Fluoride, Arsenic V and pre oxidized Arsenic III, Other residual heavy metal ions. FLUORIDE: Testing for fluoride was based on 20-30ppm of the ion in the influent aqueous solution at a flow rate of no more than 3 gpm per cubic foot of media. Results of <1ppm of the fluoride ion in the effluent were typical for the media (>95% reduction). Under optimum conditions, effluent concentrations of less than 50 ppb were readily achieved (>99.75% reduction). ARSENIC: This product uniquely targets the entire family of arsenic oxide anions as well as the arsenic cations. REPLACEMENT: Under normal conditions it is recommended that each set of two PF-2 elements be replaced after 1,000 gallons.