Harvesting fog to fight drought

It is estimated that one third of the water on earth that is not saline exists as vapour. This vapour, in its various forms, is essential in some ecosystems as a source of available water, when groundwater is in short supply.

Fog allows plants to remain hydrated in times of drought, either by condensing and falling to the ground to be absorbed through the roots or being absorbed directly into the plant’s leaves, as in the case of certain ferns growing in seasonally dry forests.

In the animal kingdom, the Namib beetle (Stenocara gracilipes) of the Namib Desert on the west coast of Africa has developed a unique way of obtaining drinking water. Its carapace has hydrophilic bumps, onto which the morning fog condenses, with the water running into hydrophobic channels leading to the beetle’s mouth, enabling it to drink.

And it seems that there are lessons to be learnt from this beetle for humans. The World Health Organization estimates that 900 million people worldwide live without access to safe drinking water. A Canadian charitable organisation, Fogquest, has been testing fog harvesting equipment in Central and South America. The fog harvesting devices have similarities with the carapace of the Namib beetle, in that they contain surfaces that both attract and repel water, arranged in a mesh formation. In field tests, these fog harvesters collected up to one litre of water per square metre of mesh per day.

Fogquest stresses that there is more to collecting water from fog than equipment alone, and it is important that the local population becomes involved, particularly the women, whose job it is traditionally to collect water. Local knowledge is also important in optimal positioning of the nets with regard to orientation, local wind variations, and fog patterns.

Although it is acknowledged that fog harvesting cannot supply enough water for an urban area, it is hoped it can make a difference to the rural poor, where much time is taken up each day obtaining water.