The operation of the AquaRain® Natural Water Filter is simplicity itself. No energy is required nor are chemicals necessary for the filter system to work. Water is poured into the upper container where it trickles down by gravity through the highly specialized ceramic filter elements leaving cysts, bacteria and ultra fine sediment in the outer layer of the ceramic. After passing through the thick ceramic wall, the water then flows through a bed of silvered coconut shell carbon which adsorbs pesticides, various organic chemicals, and chlorine (if present), along with objectionable color, tastes and odors. The filtered water then drips into the lower container where it is stored for easy dispensing with the handy lever-action faucet. Over time, small particulates and bacteria may accumulate on the walls of the elements and slow the production of water through the filter. When this occurs, simply remove each of the filter elements and lightly clean the hard surface of the ceramic with a brush or the scrub pad provided. (Unique end-of-life gauges takes out the guesswork from knowing when to replace the elements.) The elements are then reinstalled in the upper filter vessel. Proper cleaning will restore the AquaRain® Natural Water Filter to full flow rates, each and every time. Model 400: This is the flag ship of our product line which utilizes up to four high performance filter cartridges set in a 3 gallon stainless steel housing. When kept full, you can produce up to one gallon per hour of quality water for drinking and cooking. The Model 400 is about 10 inches in diameter and is 21½ inches tall including the stainless steel lid and rubber base. This unit comes with two filters and can use up to four filters.