 Inspired by Zibold 's work , Chaptal built a small air well near Montpellier in 1929 . Chaptal 's condenser was a pyramidal concrete structure 3 metres ( 9 @.@ 8 ft ) square and 2 @.@ 5 metres ( 8 ft 2 in ) high , it was filled with 8 cubic metres ( 280 cu ft ) of limestone pieces being about 7 @.@ 5 centimetres ( 3 @.@ 0 in ) in diameter . Small vent holes ringed the top and bottom of the pyramid . These holes could be closed or opened as required to control the flow of air . The structure was allowed to cool during the night , and then warm moist air was let in during the day . Dew formed on the limestone pieces and collected in a reservoir below ground level . The amount of water obtained varied from 1 litre ( 0 @.@ 22 imp gal ; 0 @.@ 26 US gal ) to 2 @.@ 5 litres ( 0 @.@ 55 imp gal ; 0 @.@ 66 US gal ) per day depending on the atmospheric conditions . 
