 In the case of small installations , convenience may outweigh cost . There is a wide range of small machines designed to be used in offices that produce a few litres of drinking water from the atmosphere . However , there are circumstances where there really is no source of water other than the atmosphere . For example , in the 1930s , American designers added condenser systems to airships – in this case the air was that emitted by the exhaust of the engines , and so it contained additional water as a product of combustion . The moisture was collected and used as additional ballast to compensate for the loss of weight as fuel was consumed . By collecting ballast in this way , the airship 's buoyancy could be kept relatively constant without having to release helium gas , which was both expensive and in limited supply . 
