A study of dew water yields on Galvanized iron roofs in Kothara (North-West India)

A dew collection project was carried out in Kothara, NW India, during the dry season between October 2004 and May 2005. One of the goals was to determine the amount of dew water that could be collected with little investment by adapting plain, uninsulated, corrugated galvanized iron roofs that are common in most rural regions of India. During the study period, the cumulative dew yield on an 18 m2 double—sloped (30°) test roof was 113.5 L (6.3 mm). The west-facing side gave 35% higher water yields than the east-facing side. The use of thermal insulation and more IR radiative materials would have increased this yield by 40% (8.9 mm or 160 L). The cumulative dew water yield remains modest when compared with the average annual rainfall (300 mm). But dew occurs far more frequently than rain and is available precisely during the dry season when water is most scarce. Dew events were correlated with meteorological data; relative humidity (the most important parameter) is strongly correlated with the monsoon.