Can fog solve water shortages?

When the rainy season ends in Cape Verde hundreds of families tap into another source of water: fog. Farmers track fog as their ancestors followed rain clouds, monitoring 15 double-sided nets that rise into the mountains.



“Here in Serra Malagueta [community of Santiago Island], like this year, there is lots of rain but we still don’t have enough from the springs,” said Domingos Monteiro, a farmer.



According to park officials, the Serra Malagueta natural reserve park and surrounding community get about 900mm of rain a year, three times the country’s average annual rainfall.



Even so, residents here have little access to safe drinking water due to a shortage of purification facilities and declining rainfall, a situation shared by 25 percent of the population - more than 100,000 people. 



Close to the sea, the government-protected park on Santiago Island has ample fog, which does not often produce rain.



With the help of 200sqm of netting erected in 2005, Serra Malagueta’s residents are collecting fog water to supply their water needs. The nets capture fog, which then turns into water that drips into a trough and flows through pipes. The filtered water is fed into holding tanks that supply the water to the elementary school and community faucets.



Before fog nets families waited during the dry season for water to be trucked in from surrounding communities that have clean groundwater, for which they paid 2 US cents per litre. 



Past droughts here have killed tens of thousands and forced many more to emigrate. Climate change experts have linked the volcanic archipelago's droughts and varied rainfall amounts to ever-warming global temperatures.



Cheap solution



Most of the country’s water must be purified at energy-intensive production plants. It costs about $1 to desalinise 1,000 litres of water, according to the government. The state electricity company spent nearly $4 million dollars on water purification in 2006.



According to the government’s June 2008 anti-poverty strategy, the state electricity and water company “faces serious difficulties in meeting the growing demand for water” and has asked larger-scale hotel operators to include water purification facilities on site.



Antonio Sabino, a local water engineer who tested fog nets 20 years ago for the National Institute of Agricultural Development and Investigation, told IRIN the nets offer a cheaper solution to cover the island’s water needs. “There is no pollution, no need for [purification-desalination] pumps, fossil fuels or motors.”



He estimated that on a windy, foggy day the 15 nets can produce more than 4,000 litres of water at a fraction of the cost residents paid for trucked-in water. Sabino told IRIN each net costs about $800, which includes labourand a filter and net screen made from locally-available materials.




Photo: Nathan Lee
The path of drinking water- a trough catches water before it is fed into pipes, a tank, and then community faucets

Hydrology risk



Portuguese engineers first experimented with fog nets in Cape Verde during the 1960s. A decade later, Dutch companies tried to revive fog water “harvesting,” but the trend again faded.



Water engineer Sabino said the risk scares people away. “All hydrology requires risks. Building fog nets require overhead investment and they may not provide as much water as expected.” But he said it is a bigger risk to not invest in alternative water sources. “Using subsoil resources without letting them recharge is like taking money out of a bank without ever depositing more money.



“Cape Verde has some zones that offer optimal [fog] conditions – some of the best in the world. The areas are small, but these small areas have enormous potential.” The engineer said Cape Verde’s more than 1,000 hectares of land is sufficiently foggy to produce billions of litres of affordable clean water per year.



Currently Serra Malagueta is the only community doing fog-harvesting.



Problems



Starting in November, Saharan desert winds from northern Africa blow dust onto the nets, making it harder to ensure water quality. Sabino said it is important during this period to change the filters, clean the nets and check water quality.



Also, there is not year-round fog in Cape Verde, which markets itself as a sunny tourist destination. “Nets should be built with sufficiently large dimensions to produce enough water to accommodate these periods,” advised Sabino.



Finally, Sabino dismissed occasional complaints about the nets’ appearance. “I don’t believe in this notion that tourists will think it is ugly. The objective of the [nets] project is to produce water to give people to drink. Not to take pictures.”



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