City of Cape Town fog harvest
Table Mountain fog harvester (Image supplied: City of Cape Town)
  • A lone fog harvester has been built atop Table Mountain for the purpose of a feasibility study.
  • Capturing moisture as fog passes through the mesh weave, this technique has been used in other parts of the country to provide drinking water.
  • Results from the Table Mountain programme will only be known in 2023 and, until then, hikers have been warned against drinking from the harvester’s reservoir.
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Although dams feeding Cape Town may currently be at capacity following full winter rains, the not-too-distant memory of drought, water-restrictions, and a looming day zero have kept City officials on their toes. In exploring all options to supplement the area’s primary water supply, a fog harvesting project has been established on Table Mountain.

Harnessing condensation, through large mesh nets, for drinking and supplying non-potable water for agricultural purposes is nothing new to South Africa. Within the context of the Western Cape, however, this fog harvesting pilot programme, perched almost 800m above the city on Table Mountain’s plateau, could provide a vital answer to the region’s intensifying water woes.

Phase two of the Table Mountain project was recently unveiled by the City’s Mayoral Committee Member for Water and Waste Alderman Xanthea Limberg. While still in its infancy, the programme hopes to determine the feasibility of constructing multiple fog catchers on the mountain. Limberg noted that the City’s Scientific Services Branch would closely study water yields over the coming months and years.

“City officials are willing to think outside the box, and this is so important for ongoing adaptability and resilience,” said Limberg, who added that the feasibility study and research phase would be completed by December 2022. “The more we research and understand, the stronger and better prepared we become.”

City of Cape Town fog harvest
Table Mountain fog harvester (Image supplied: City of Cape Town)

The first official studies concerning moisture density on Table Mountain were conducted over a century ago by German-born botanist Rudolf Marloth. Studies conducted since then have placed yearly fog precipitation at around 3,294 mm, triple the average yearly rainfall recorded in Cape Town. The mountain’s famous ‘tablecloth’ – scientifically referred to as an orographic cloud formation – is responsible for much of the high-altitude moisture and optimism surrounding the fog harvesting programme.

Thinly spaced polymer mesh, held upright by stainless steel poles, collects collect the moisture of fog which passes through it. These water droplets are then channelled into a reservoir.

“All visitors using the Cable Car will be able to see the phase two site, which has a sign up that explains the project to the public,” explained Limberg. “Hikers are asked to please keep their distance, and to avoid drinking the water as it has not been treated.”

Fog harvesting projects, mainly for use in small communities and agricultural applications, have been implemented with positive results in the Northern Cape, Eastern Cape, Mpumalanga, and Limpopo. Pilot programmes along South Africa’s arid west coast, revealed average daily yields of 4.6 litres per square metre of collecting surface. The Water Research Commission said that maximum daily yields of this relatively small pilot programme could reach 4,000 litres.

"The technical aspect of this research project cost has been R350,000 for the engineering/technical skills and equipment required, covering both Phase 1 and Phase 2, and it is being run by the City’s in-house staff scientists," explained Limberg. "The volume of water which can potentially be produced will only be able to be determined in about 12 months."

Water consumption in Cape Town hovers around 700 million litres per day.

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