City of Cape Town reevaluating fog harvesting plan for Table Mountain

The City of Cape Town has shared an update on what was happening with its fog harvesting plans, which was first initiated amid the panic of the City and province’s water crisis.

While “Day Zero” may be a thing of the past, it introduced a hyperawareness to the water supply challenges that the province faced.

“Day Zero” referred to the day when most of the taps in Cape Town would be shut off, and residents would be forced to queue at some 200 water collection points for their allocated 25 litres of water per day.

That day was meant to be April 12, 2018.

The term “Day Zero” was added to the lexicon of many Cape Town residents, and tourists, when the province experienced the worst drought recorded in its history, which in turn, led to the 2017 and 2018 water crisis.

Back in December 2020, the City announced that as a result of the drought shock, the implementation of desalination, water reuse, and aquifer abstraction had been implemented at an accelerated rate.

One of the projects they investigated looked into the potential of using fog to directly or indirectly augment the drinking water supply.

As the City shared their lessons that they learned 7 years on, they also shared what became of their fog harvesting project - which refers to the collection of fog (water) from the atmosphere.

The City explained that the principle of fog harvesting is based on the fact that air contains a certain amount of water vapour, originating from ocean evaporation.

At higher temperatures, air contains a larger volume of water vapour than at lower temperatures. As air is transported up a gradient by wind, it interacts with colder air and is condensed into fog.

“Key ingredients to the favourable formation of fog are high altitude mountains (> 800m above sea level) within close proximity to the coastline.

“The technique has been used for decades in dry and isolated regions, such as in Chile, Peru, and Spain, though mostly managed by research/academic institutions as opposed to a municipal scale,” the City said.

“Various studies had been conducted on fog harvesting for domestic water supply purposes elsewhere. Most of the studies involved the use of a polymer mesh or shade cloth, kept in an upright position by stainless steel poles, that collects droplets as the wind blows the fog through the mesh. Droplets then trickle into a collection chamber.”

Mayco Member for Water and Sanitation, Zahid Badroodien said two sites were identified for the project.

Site 1 was located at 714 metres above sea level near the Woodhead Reservoir Conference Room, which commenced in 2018. Site 2 was situated at 1 000 metres above sea level near the Table Mountain cable car station, which began in 2020.

“Site 1 was decommissioned in 2023 due to low water yields and logistical communication challenges.

The pilot aims to answer several key questions: whether the harvested water complies with SANS 241-1:2015 drinking water standards; whether the water is chemically stable (i.e. corrosive or scale-forming); and whether the Table Mountain environment is suitable for long-term fog harvesting operations.

“The City is currently in the process of reevaluating these factors to determine the overall viability of the project,” Badroodien said.

“The continuation of Site 2 will depend on the outcomes of this review, including the consistency of water yields and the practical feasibility of expanding the system.”

Badroodien said that the City remains committed to exploring innovative and sustainable water solutions in support of long-term water resilience.

“The City is actively investing in its New Water Programme to diversify its water sources and build a resilient supply so that we can reduce our dependence on unpredictable rain-fed dams and navigate future climate change shocks.

“The City is committed to investing annually in its water and sanitation infrastructure to ensure that our residents continue to benefit from reliable services,” Badroodien said.

He said that Cape Town is investing more in infrastructure than Johannesburg and Durban combined, with a capital budget 91% larger than Joburg and 117% larger than eThekwini over the next three years.

“Water and Sanitation represent 42% of our approximate R120 billion 10-year infrastructure pipeline, funding critical projects from our New Water Programme that will produce 300 million litres of drinking water daily by 2030.

“Unlike other metros, Cape Town is proactively securing its water future through innovative solutions that ensure resilience against climate change and population growth.”

theolin.tembo@inl.co.za