Venetian Wells

If you have been to Venice, you have probably noticed the often intricately carved well heads in the center of nearly every campo.  Since Venice is very nearly under the salt water which fills its canals, it would seem unlikely that a simple well could provide potable water.  As it happens, they are not wells at all, they are cisterns which collect and filter rainwater.  Basically, the Venetians excavated the plaza to a depth of around 10 feet in the form of an funnel.  The hole was then lined with clay.  The well was situated at the deepest part of the clay funnel and constructed out of porous bricks without mortar.  The area inside the funnel and around the well was then filled with sand and covered with brick or stone.  Rainwater would flow off the roofs of the city's buildings into storm drains in the plaza where it would flow through the sand (filtering it) and fill the clay cistern.  Clean water could then be brought up through the well mouth.