18-06-2025
Avoiding Day Zero in Gauteng — a comparison with Cape Town's success story
The phrase 'Day Zero' has come to mean that precise moment when a city's water supply is predicted to be depleted, leaving taps dry and local economies in crisis. It entered the global lexicon in 2018 when the City of Cape Town was confronted with an acute water crisis.
The actual Day Zero was estimated to be in April that year, with three different dates, depending on the models being used. With a population of more than four million people requiring water, the city's executives were forced to implement strict water reductions on the public and corporations in the city.
With these severe water restrictions, the city was able to replenish its water resources and it announced that 'Day Zero' had been averted.
That single event captured the attention of the global media, which ran stories in many countries. It has now triggered the XPRIZE after the Mohamed bin Zayed Water Initiative offered a $119-million cash incentive to radically alter the future role of desalination technology solutions.
Cape Town managed to avert its Day Zero crisis through an aggressive review and application of innovative policy, supported by intensive communication designed to build consensus, retain social cohesion in times of crisis and change human behaviour.
But trust in the government was eroded and is unfortunately still in deficit, as is manifested by the festering issue of sewage discharge into aquatic ecosystems. Analysis of this strategy has shown that water security requires a mix of solutions, with no single silver bullet being viable.
A water secure Gauteng
These lessons have been fed into the Platform for a Water Secure Gauteng (PWSG), which has been created to avoid Day Zero in the heart of the South African economy.
A lot of the energy that fuelled the Day Zero narrative was hype, and the one lesson that I have learnt from three decades in the international water sector is the role of nuance in every water-related problem.
In short, things are always different in various geographic locations, so I have become sceptical of simple silver-bullet solutions, often touted by over-enthusiastic solution-providers that seldom understand the complexity of the problem being managed.
It therefore becomes instructive to compare the differences and similarities between Cape Town's and Gauteng's Day Zero narratives. Facts are our friends, so let us embrace a few of the most important ones.
For starters, both the Western Cape and Gauteng regions are supported by a complex arrangement of institutions, dams, pumps and pipelines, so that is a good point of departure.
The Western Cape Water Supply System (WCWSS) stores 890 MCM (million cubic metres), which is two years of average water supply needed for the city of Cape Town and the local economy.
There are several dams, including Theewaterskloof, Voëlvlei, Berg River, Wemmershoek, Rockview, Kogelberg and Steenbras Upper and Lower, some of which are interconnected by pipelines, tunnels and distribution networks.
The rainfall is naturally a winter event, so storage is needed for the long summer months. Water is cascaded into this system through a series of inter-basin transfers from an adjacent water management area.
Now let us compare this with the Integrated Vaal River System that sustains 45% of the South African population and 60% of the national economy. There are a total of 14 major dams, with the most important shown in the diagram, which also indicates the depth of each and the degree of interconnectedness across the whole system.
It is managed as a single entity and it has a total storage capacity of 10,554 MCM (million cubic metres), which is about six years of average supply under non-drought conditions.
Water is sourced from many different river basins, including the Tugela in KZN and the Malibamat'so in Lesotho. This water is diverted over the Drakensberg Mountains into the Sterkfontein Dam in the case of the Tugela.
The energy needed to pump these massive volumes uphill is taken from the Eskom grid as part of a pumped storage scheme needed to put electricity back into the grid during peak energy demand. This problem is solved in the transfer of water from the Katse Dam in Lesotho, where the Muela power plant generates electricity using the constant natural flow of the system.
When comparing the two systems, achieving water security in Gauteng is significantly more complex than in Cape Town. This highlights the challenge faced by the respective water boards in each case.
Rand Water is one of the largest bulk water suppliers in the world, responsible for guaranteeing water security for almost half the population and two-thirds of the national economy.
The challenge in Cape Town is defined by the limited strategic storage of two years. Cape Town is on the coast, so sea water desalination at utility scale (bigger than 50 megalitres per day capacity) is the obvious long-term solution, along with the recovery of water from waste.
Both options are part of its strategic plan to achieve water security, with the latter being implemented in a groundwater recharge programme, like the city of Perth. The challenge is restoring public trust and investor confidence damaged by the Day Zero crisis in 2018, but exacerbated by the city's response to public concerns over sewage discharges into aquatic systems such as Milnerton Lagoon.
Gauteng's complex challenge
The challenge in Gauteng is different and more complex, so Rand Water will be confronted by demands on its decision-making capacity on an unprecedented scale.
I have previously written about the sewage challenge (see Understanding the sewage challenge facing Gauteng's water supply), suggesting that Rand Water might have to start considering the recovery of water from waste to achieve two outcomes – mitigate the risk of sewage pollution of the Vaal and augmentation of supply to industrial users that might not need potable water for their processes.
Gauteng will also be forced to consider the desalination of acid mine water, and this is where their challenge differs from Cape Town. About 200 megalitres of water can be recovered from acid mine drainage, but the Capex cost will be in the vicinity of R15-billion, with an annual Opex cost of around R2.5-billion. Those are big numbers for a relatively small increase in supply.
Furthermore, the disposal of brine is not possible on the Highveld as there is no sea into which it can be discharged. For this reason, desalination is likely to remain non-viable for Rand Water.
The good news is that the salinity levels of acid mine water being discharged into rivers is slowly declining, which adds value to the decision not to desalinate.
The important take-home message is that maintaining water security in Gauteng will place growing demands on Rand Water in a manner unparalleled by any other water board in South Africa.
Its institutional architecture will have to adapt to new business models capable of responding to a set of challenges that will increasingly differ from what it has faced in the past century of its existence.
The institutional health of Rand Water will be of increasing importance, so it is in our collective best interest to support it in any way possible. DM
