Water Portal / Rainwater Harvesting / Fog and dew collection / Dew collection and storage

Dew Collection and Storage

Dew can bring substantial amount of water when the other resources (groundwater, rain, fog) are lacking. Rainwater harvesting structures can also be used to collect dew at night, which condenses on a surface from where water droplets drip into a gutter that goes to a reservoir. Quantity from dew varies according to location but at times has been shown to constitute a significant proportion of normal rainfall. Dew collection is a possible supplementary source of water in arid and semi- arid areas, but has so far not been widely applied and is an area of further research.

Suitable conditions

• Large areas of unused land.
• Areas with large diurnal temperature range (at least 12 degrees Celsius from day to night).
• Areas with low winds (winds cause evaporation). It is advised to have an upper limit of 4 m/s at 10m.

The average wind speeds where dew forms correspond to rather large speed (1-2 m/s), higher than ones found in continental locations of 0.1 - 0.2 m/s.

• Dew yields are seen to rise when cloud cover diminishes because the radiative cooling increases.
• The largest dew yields correspond to the highest humidity and the lowest cooling temperature.
• The condensing material must be adequate (thermally isolated, water resistant, on a slope).

Experimental dew condenser in Vignola (Corsica island, France)