These most antique stoneware ceramic water filter systems by Cheavin's Saludor (British), circa 1950s, was popular at a time when chlorine treated water was not a norm. Doctors and dentists have been known to use them. For a household to own such a filter in those early days was a social symbol of well being. Filter works on principle of passing untreated water through cyclindrical carbon filter tube in the inner canister. Carbon contains ions that kills germs working on principle of absorption. Gas and other offensive taste in water too stick to the carbon filter tube resulting in "spring water" for consumption that can easily be released from tap at bottom of outer canister. Each doomed lid has an interior ridge to prevent it from slipping off from canister. Selling as set of 3 for $1500.00. Ps : Willing consider break up sale. Size X 56cm height, 24cm dia @ $650. Size W 50cm height, 22cm dia @ $550. Size V which does NOT hv inner canister anymore, 44cm height & 19cm dia @ $350.