 An air well requires moisture from the air . Everywhere on Earth , even in deserts , the surrounding atmosphere contains at least some water . According to Beysens and Milimouk : " The atmosphere contains 12 @,@ 900 cubic kilometres ( 3 @,@ 100 cu mi ) of fresh water , composed of 98 percent water vapour and 2 percent condensed water ( clouds ) : a figure comparable to the renewable liquid water resources of inhabited lands ( 12 @,@ 500 km3 ) . " The quantity of water vapour contained within the air is commonly reported as a relative humidity , and this depends on temperature — warmer air can contain more water vapour than cooler air . When air is cooled to the dew point , it becomes saturated , and moisture will condense on a suitable surface . For instance , the dew temperature of air at 20 ° C ( 68 ° F ) and 80 percent relative humidity is 16 ° C ( 61 ° F ) . The dew temperature falls to 9 ° C ( 48 ° F ) if the relative humidity is 50 percent . 
