The authors have developed a “Earth-Air Heat Exchange Distillation System” for collecting water from vapor originated in evapotranspiration. This system distills water from vapor by cooling the air in a greenhouse, using underground heat exchange pipes. It is similar to “Soil Heat Exchanger-Storage Systems”. A parameter for estimating the daily amount of collected water was investigated, based on heat and vapor budget of the heat exchange pipe. The results indicate that the daily amount of collected water is a linear function of the integrated surplus of air-soil temperature.