Humans usually source water from rivers, wells, ponds or underground aquifers. All these sources are ultimately fed by rain (scientists prefer the word 'precipitation'). But there exists another, lesser known, source of water: occult precipitation, the water one gets from fog.
What is fog? It is a mass of water vapour condensed into small droplets, 1 millimetre (mm) to 40 mm. As it rolls in like a white blanket, say in a forest, tree leaves harvest it. The amount harvested depends on how 'wet' the fog is (how heavily laden with water it is). It also depends on the frequency with which it occurs in an area, and whether it is a strong or weak wind that causes the fog to roll in, swish about and disperse, or hang about enveloping everything in an eerie whiteness.
What is 'occult' about a droplet of water that forms on a tree leaf (or, as we shall see, on a net)? Nothing, except that it is quite an esoteric way to collect water. Look at it this way. Rivers, ponds or underground aquifers are overt sources of water. They are out there, readily available, known to be so because seen to be so, obviously used. (Of course, some could argue that the only overt source of water is the 500- or 1000-litre booster-fed tank that sits like a black mole on house terraces. They wouldn't be wrong, would they?) In contrast, fog is a covert source of water. A little hidden, a little out of the way.
But that doesn't mean it is an arcane or mysterious source of water. Ask the villagers of Chungungo in coastal Chile, or that of Danada Bazaar in Nepal. As Robert Schemenauer, executive director of FogQuest puts it, "It is not a new idea. There is a long history of people experimenting with fog to ensure potable water."
To collect fog, you need a fog collector. A simple net put up against the direction of the prevailing wind, or a series of such nets. The mesh material is normally nylon or polypropylene, and the mesh's thickness could be 1 mm or even 0.1 mm. The mesh is weaved in triangular shape, with the strings spaced out at 1.3 centimetres.
Take then this mesh and tie it to two posts (called the collector frame, not too far spaced out) in a double layer. Make sure there is a trough underneath. Then wait for the fog to roll in. The trough will slowly fill up with droplets of water. Route the water to a storage tank.
Fog collectors work best along coasts (where the fog seasonally rolls in from the sea, or ocean), and in mountainous areas where water is present in stratocumulus clouds at altitudes of 400 metres to 1200 metres. The mesh, if maintained, can last 10 years.
The largest project to date (now defunct) provided 11,000 litres of water daily. This happened in Chungungo, a village of 330 people in the arid coastal desert of northern Chile. The villagers used to get their water trucked in at a cost of
us $8 per 1000 litres. In 1987, the government of Chile asked a Canada-based non-profit organisation called FogQuest to consider if fog could be collected. By 1992, there were 75 fog collectors along the ridge that separated the village from the ocean. A 6 km pipeline brought water to the village, and 106 households had a much-welcome additional source of potable water. Because the system was unconventional, and the money came from Canada, a non-standard organisational structure evolved at the village level to manage the fog collection.
The system is defunct today. As Schemenauer says, "Chungungo has prospered with the addition of the fog water supply. Now they are exerting political pressure on the regional government to give them a water pipeline from a source 40 km away at the cost of
us $1 million. (A project with 40 large fog collectors, reservoirs and pipelines might cost
us $35,000.) It appears that they are letting the fog collector system fall into disrepair to pressurise the authorities."
British architect Matthew Parkes credits the Stenocara beetle for inspiring him to design a nylon mesh to collect water from fog. The beetle, generally found in the deserts of southwest Africa (Namibia), lives in an environment of high winds, extreme daytime temperatures and dense morning fog. In the morning, the beetle tilts its body towards the wind. Droplets of water form on its fused wings and roll down the body towards its mouth.
In the Cape Verde islands and the Sultanate of Oman, fog is collected from trees. In the Dhofar region of Oman, olive trees act as vertical barriers. The yield here varies from 580 litres to 860 litres per day. The trees experience fog and light drizzles for about 80 days in a year. Similarly, the families and school of a village in the Salagnac Plateau in south-western Haiti have overcome their winter water shortage by installing fog collectors at an elevation of 1000 metres. Today each cubic metre of mesh produces about 165 litres of monthly supply from both fog and occasional rains.
With help from FogQuest, a Water from Fog project began in the village of Danada Bazaar, at an elevation of 7,000 metres, in eastern Nepal. The beneficiaries are 15 households.
Why isn't there more of fog-collection? Feels Schemenauer, "It is always difficult to introduce unconventional technologies. Also there has been no large funding source to promote the technology and to fund large new projects." Perhaps another reason is that fog collection is impossible to conceive without the interest of local communities. Couldn't it be done in India, say in the Western Ghats or in hilly northeast India? Yes, feels Schemenauer. (He feels fog can be collected wherever the right conditions exist.) Not needed, says C K Varshney of the School of Environmental Sciences at the Delhi-based Jawaharlal Nehru University: "We don't need human-made nets as we are already collecting water through our vegetative cover. We should focus on how to optimally manage the rain."
