Venice‚Äôs underground does not have easy-to-reach water tables. Up to a century ago, fresh water was drawn from the springs on the mainland and transported in casks to the lagoon by boat. This supplemented the traditional rainwater collection system built in the campi and campielli: it consisted of a wellhead and an underground cistern, filled with clean sand, with a waterproof layer of clay all around that served as a barrier against the infiltration of saltwater.
The rainwater penetrated into the ground by means of collectors positioned around the well, located at slightly lower levels than the rest of the campo; it filtered through the sand down to the waterproof clay bottom of the cistern. The well shaft, which was waterproofed by a layer of clay (tera da sa√≤n, soap earth) spread along its entire length, filled up from below with the collected water, which had been purified as it drained through the sand. The water was drawn with buckets.