Harvesting Water from Fog
Where there's fog there's water--lots of it! Now a climatologist from the University of South Africa (Unisa) has helped develop a low-cost, ecofriendly system to harvest moisture from abundant mountain fog in a water-scarce region of South Africa's Eastern Cape, and communities there are already benefiting from it. The project was successfully launched in Cabazane Village, in the rural Mount Ayliff area in the north of the province, in mid-March 2010 during the annual National Water Week.
The area, in the picturesque Alfred Nzo district municipality, is bordered to the north by the mountain kingdom of Lesotho and much of the terrain is steep and remote, with very cold winters and mild summers. Fog is a frequent visitor and a ready source of clean water. Professor Jana Olivier of Unisa's School of Agriculture and Environmental Sciences has spent the past 20 years specialising in the properties and hazards associated with fog, especially for vehicles.
She later started delving into the technique of fog harvesting. "We got funding from the Water Research Commission, and we designed the fog water system," she said. Olivier teamed up with Professors Johan van Heerden, Hannes Rautenbach and Tinus Truter--all of Pretoria University--in the development of the system.
However, the system is only practical where fog occurs for at least 40 days a year, and for a period of several hours at a time.
The project has also been rolled out in other dry areas of South Africa, including Venda, Limpopo, and the West Coast, but Mount Ayliff s persistent fog yields the best results, producing hundreds of litres a day.
"The West Coast and the mountainous areas--stretching from the Soutpansberg in the north, along the Drakensberg in the east to the Cape Mountains in the south--have the highest fog harvesting potential," said Olivier.
Mount Ayliff is located in the Umzimvubu local municipality, one of two municipalities within Alfred Nzo. Its population is just 198,550, of which only 4% live in towns. Safe drinking water is a persistent problem. Villagers are often forced to dip into natural springs, running the risk of contracting water-borne diseases. However, the villagers' lives have changed with the installation of the water-harvesting system and its inexhaustible supply.
No electricity is needed to power the scheme, which makes it ecofriendly and low cost, and suitable for areas with no power infrastructure. Because the technology is simple, the equipment does not need special maintenance. The system consists of a double layer of 30% shade cloth nets stretched between steel cables supported by posts, with a gutter beneath each screen to catch the run-off. The Cabazane set-up involves around 700[m.sup.2] of netting, says Olivier, with each square metre of shade cloth yielding up to five litres of water a day--depending on the weather.
Water droplets in the fog are trapped on the nets. They get bigger and heavier as the fog rolls along, and eventually run down into the gutter and from there through a filter into storage tanks. …