The most powerful gravity-fed element in the Filtration class. Filtration class: Micro-Filtration Technology. Tested to reduce contaminants to bacterial level. Chemicals, herbicides, pesticides, VOC's, THM's, heavy metals and more are easily reduced to 99.9%. Proprietary formula comprised of Diatomaceous Earth, granulated activated carbon and other media components, designed to exceed filtration standards. Each element will filter up to 3, 0ls of water or last up to 3 years, before replacement is needed. With 4 elements (in a Big Berkey system), the 18cm elements can produce flow rate of up to ÃÂÃÂÃÂÃÂ 0ls per hour or up to 0ls of water in 24 hours. Ideal for the price-conscious consumer to get started with a highly efficient filter system, at a more affordable price. Economical entry price affords those who would like to upgrade to the more powerful Black BerkeyTM elements down the road, the ability to get an effective and economical system now and then upgrade later. Available in 18cm and 23cm sizes. Compatible with PF-4 Fluoride and Arsenic Reduction Filters.