 Klaphake experimented with a very simple design : an area of mountain slope was cleared and smoothed with a watertight surface . It was shaded by a simple canopy supported by pillars or ridges . The sides of the structure were closed , but the top and bottom edges were left open . At night the mountain slope would cool , and in the day moisture would collect on and run down the smoothed surface . Although the system apparently worked , it was expensive , and Klaphake finally adopted a more compact design based on a masonry structure . This design was a sugarloaf @-@ shaped building , about 15 metres ( 49 ft ) high , with walls at least 2 metres ( 6 ft 7 in ) thick , with holes on the top and at the bottom . The outer wall was made of concrete to give a high thermal capacity , and the inner surface was made of a porous material such as sandstone . According to Klaphake : 
