The Gravidyn is a free-standing, no-pump gravity filter that uses 3 ceramic, carbon-filled filters. Activated carbon improves water flavor and lasts for up to 6 months. The ceramic filters (0.2 micron ceramic depth) are cleanable and last much longer. The ceramic outer walls (0.2 micron ceramic depth) block protozoa AND bacteria with its 0.2 microns filter wall (2 ten-millionths of a meter). Silver particles are impregnated into the ceramic before baking to provide a bacteriostatic filter wall. Due to its ceramic wall, the filter can be cleaned many times - even out in the field (abrasive pads included). The ceramic stage can filter up 13,000 gallons of water (much less in turbid water). The second stage of filtration uses activated carbon to remove pesticides and chemicals and to improve water flavor. Carbon cores remain active for up to 6 months after first use, but the ceramic wall continues to filter harmful microorganisms long afterward. This drip filter is used by international relief organizations as group equipment for preparing water. It is also ideal for use in emergencies, hunting, fishing and cabins.