Harvesting dew to supplement drinking water supply in arid coastal villages of Gujarat

Abstract

Shortage of drinking water is chronic, sever and widespread in Kutch - a hot and very arid region. It is specially acute in coastal villages where surface sources dry up rapidly and groundwater is not potable. Many of these are listed as “no source” villages and are supplied water on tanker-trucks daily from long distances. The conventional efforts to conserve and augment water resources are all in place. But one potential resource - dew - had remained unnoticed. The possibility that it may also be a supplementary resource was first noticed in the summer of 2001 when it was observed that dew condensed frequently on a plastic- clad greenhouse in Kothara, a village 15 km from the coast. That led us first, to carry out systematic measurement, and then to develop practical ways to harvest dew for human use. Measurement at Kothara was followed by measurements at two other locations along the coast - Panandhro and Mithapur. Data showed that dew occurred over an eight-month season (October- May) spanning the entire dry part of the year. Quantity was more in summer months than in winter. Dew water was found potable and safe. In the next three years development of dew harvest systems was carried out, prototypes were made and tested. After successful field trial three models were launched. The key component of the systems is the condenser, made of thin plastic film which can harvest 15 – 20 mm of dew water in the season. Condenser cools itself by radiative exchange with sky, without the use of any external energy. Working installations have been made on large roofs and on open ground. While the devices are specifically engineered to condense dew, these routinely harvest rain as well. These are being promoted as “dewrain” harvest systems that deliver useful but varying amount of water through all the months of the year.