Why “MAR” is Essential to Cape Town’s Water Survival

“MAR” meaning Managed Aquifer Recharge

We have been hearing about Cape Town’s water woes and a second potential “Day Zero” and how it plans to navigate through the dry season until it can again naturally regenerate its resource base. The Western Cape, and especially the City of Cape Town has always utilised above open ground resources such as dams, rivers and reservoirs, but with the influx of people from other provinces of South Africa – as well as the waves of European Retirees settling in the Overberg Winelands and Coastal areas to enjoy their twilight years – the existing infrastructures are being swamped. The demand for water is far outstripping the available supply resource. Already in February our dam levels have slipped to under 60% and at present usage level exceeding 1billion litres of treated water through the various municipal treatment works PER DAY!  The City of Cape Town are targeting a reduction of +/-7.5% to 955 million litres per day, but even should this is achieved, above ground water sources will be inefficient to supply the demand of its Consumers.

Beyond Dams: Tapping into the TMG and TMZ Aquifers

Cape Town has a trump card up it’s sleeve in that although there is no current available facility that it can adapt into a substantial above ground water storage site, it sit’s above the massive TMZ aquifer (Table Mountain Zone) part of the enormous TMG aquifer (Table Mountain Group running from Van Rhynsdorp in the North, Agulhas in the South and East as far as Uitenhage) which it is planning to eventually over up to 50million litres per day from various wellpoints across the field. They are already extracting between 20 – 25 million litres from their Steenbras operation at present. 

However it might be unwise to trade a short-term fix and put off long term resultant problems without examining all the facts and figures. 

The TMG aquifer covers a huge area (about 11 000 km² in the Western Cape) and extends to >1 000 m depth in many places. It is estimated to contain a recoverable 50000km³ of ground water within 200km of Cape Town, that is a staggering 50 billion m³. This seems like a very good deal for the City of Cape Town, however the aquifer is deep – present well depths range from 150m to 350m below ground level. If the City of Cape Town want to radically increase their yields, it is estimated by some that the drill depths will be up to 710m below ground level with some horizontal directional drilling (HDD) to avoid igneous rock strata’s.

The Risk of Over-Extraction: Saltwater Intrusion & Contamination

Another major environmental consideration would be the recharging of the sub-terrain water pumped out from the aquifer. Just the same as it is not being extracted naturally – ie a spring point – it also cannot be recharged naturally. Typically, ground water will take anything from a decade to 1000’s of years to seep through the different rock stratas just to a level of 100m below ground layers and this increases exponentially when it encounters igneous quartz layers, on which much of the Western Cape sits.

So why can’t we merely leave a space above the water table? With the strong quartz sandstone cover it shouldn’t collapse. This is a question few want to bet their reputations on, but more importantly there is another factor that outweighs even that problem, and that is the problem of cross contamination.

As fresh water is absorbed by the soil and rock strata’s, sea water is also absorbed through the sea bed and the various strata’s encountered, However due to a difference in the specific gravity between fresh water and salt water of 1 :1.025, the salt water would normally be absorbed faster and reach specific depths faster in comparison to fresh water. 

When taking the geographical closeness of the TMZ to the coastal saltwater aquifers – together with the extreme depth of the TMZ aquifer estimated to or in excess of 1km into consideration there is a good possibility that if the aquifer is not recharged, then salt water from the adjacent coastal aquifers will start to leach into the freshwater source. Small amounts of saltwater seepage will obviously happen but that should be kept to an absolute minimum to avoid permanently poisoning (via salt intrusion) the resource.

What is Managed Aquifer Recharge (MAR)?

This is where Managed Aquifer Recharge (MAR) should be strategically applied by the City of Cape Town to ensure that the resource is maintained for future generations. The City Council has published certain strategies to enhance water security, sustainability and create a robust and resilient plan of action to ensure the longevity of the resource which involve the following: –

Wetlands

• Ensure that existing wetlands are protected from urban expansion and ensure that the ecological balance remains as unaffected as possible from the human presence surrounding it.
• To dedicate new protected lands especially adjacent to existing wetlands for the purpose of increasing the percentage of wetlands usage to vacant available land in the coastal Western Cape.
• Ensure that all large volume housing complexes try to form in-house wetland reserves or open grass detention ponds to hold seasonal deluges (which in open street residential areas would go to storm water drainage and in Cape Town be vented into rivers which estuary within 20km into the sea)

Selective Wellpoint placement

• To ensure that a sufficient distance between individual wellpoints is maintained so as not to deplete certain areas and spread the load across the aquifer as a whole and avoid over abstraction.
• Use hydrogeological modelling to predict water levels under varied abstractions and climate scenarios — helping prevent depletion. 
• Monitor extraction rates (both municipal and private) and recharge balance to ensure the aquifer isn’t stressed beyond natural replenishment limits.

Integrate Groundwater with Other Water Sources

• Diversification = Resilience. Groundwater from the TMG aquifer should be part of a portfolio of sources that also includes dam water, direct potable reuse, desalination, surface water and rainwater harvesting. 
• Blending groundwater with treated surface water at plants (e.g., Faure treatment works) ensures consistent quality and reduces strain on any single source. 

Strengthen Governance, Monitoring and Regulation

• Data-driven water management systems deploying sensors and digital platforms that track aquifer levels, extraction volumes, quality changes and recharge success in real time.
• Regularly update groundwater models and adjust abstraction permits based on changing climate and usage patterns.
• Introduce policy and planning improvements, align groundwater use with integrated water management plan ensuring environmental, agricultural, domestic and industrial needs are balanced. 
• Enforce protection zones and development controls around sensitive groundwater catchments to avoid contamination and land-use conflicts. 

Integrating Groundwater into a Resilient Water Portfolio

Implementing the MAR strategically

Simply put, this would mean ”replacing what is taken out” and ensuring that checks and balances are in place and adhered to. The City of Cape Town plans to “supercharge” it’s MAR strategy by intentionally injecting highly treated wastewater and stormwater into aquifers. These recharge projects would act:

• together with natural replenishment and utilise normally discarded resources to fill up aquifer water levels when the water draw is low (the winter wet season), so that in the summer months, when the demand is at its highest, there is sufficient volume to meet the requirements;
• to ensure that new and highly efficient wastewater treatment plants are established with quality-protection mechanisms firmly in place. Any water that is allowed to enter the aquifers must be of a high quality – chemically and microbiologically – so as not to poison the aquifer, as once this happens it would be almost impossible to reverse;
• to increase the scope of the resource holding capacity through the branching of major waterways via culverts either to existing/new wetland areas, or to create a series of new retention dams prior to these waterways/rivers progress into the estuary area and thereafter the sea;
• provide newly created wetland areas with specific plants known as hydrophytes which thrive in environments with low oxygen levels, fluctuating water levels and waterlogged soils. (either “emergent” – rooted in saturated soil with stems rising above the water level, “submergent” where the plant survives fully under water or “floating” with stems and leaves at the water’s surface. This vegetation cover will help bind the soil substrata and lessen natural water loss via evaporation;
• to divert as much of the stormwater from urban and residential areas which at present runs straight into the sea to retention dams and areas of expanding wetlands;
• stricter legislation with closer co-operation with industry, especially if cited on or close to the aquifer catchment area. This would ensure that industrial contaminants, oils, chemical based effluent etc is not released into any common waterway or vacant land;
• preventively harsh punishments must be strictly enforced, or we will see the TMZ aquifer asset turn into the poisoned wells such as those of the Witwatersrand;
• stricter legislation with closer co-operation with the agricultural field, especially if cited on or close to the aquifer catchment area to ensure that chemicals, phosphates, insecticides and pesticides are not released into any common waterway or vacant land
• stricter control of urban runoff and general pollution where waterways run through or alongside RDP or informal urban developments with stepped weir catchment sites where solids can be easily removed from the water flow and
• use dynamic supply optimisation models so City engineers can switch between sources depending on rainfall, usage and recharge levels

The Infrastructure Challenge: Fixing Leaks and Protecting Resources 

However, even if all the Western Cape’s water resources combined are responsibly and efficiently managed, that would not let the Province “off the hook” regarding the future water supply situation. 

Infrastructure is still an enormous problem with well over half of all repairs and maintenance being dealt with on an emergency basis instead of being planned and scheduled on an ongoing basis. Many of our major piping works are far older than the recommended 15-year life cycle, and the efficiency at our wastewater plants, although probably the best in South Africa are still a far way from the European norm if it were it would’ve allowed us to reutilise wastewater up to potable water standards. Bear in mind that, the Western Cape’s population is set to increase by 10% over the next decade so our already stretched systems and infrastructure will be sorely tested

We should therefore start planning and instituting steps and measures immediately to ensure “day zero” never happens.

Through water-wise education of Residents, Commerce and Industry and the introduction of low-flow fixtures, recycling of household and rain water for gardens and highlighting the problem of leak detection (a running WC valve can waste up to 7 kl per month), such education can be backed up through constant public awareness programs and visible rewards  on Resident’s municipal accounts for actively cutting usage. When used in conjunction with implementing tiered pricing to discourage waste and incentivise conservation. It is also very important to educate the populace on the necessity on protecting ground water together with its recharge areas and to be more responsible with litter and other contaminants.

Finally, the never-ending task of the Municipalities to maintain and service their delivery reticulation systems. A mindboggling 60% of all water treated to potable standards throughout South Africa never reach the Consumer. These losses occur due to leaks within main supply pipes between Urban centres where identifying the position of the leak is extremely difficult due to the long uninhabited distances involved. Although initially expensive maybe metered valves could be installed at individual pump stations where the physical flow of water through  the pipe is monitored, then if pump station (a) registers a flow of 50kl but pump station (b) only registers a flow of 40kl, the it can be logically assumed that there is a leak between (a) and (b).

News Flash – News Flash – News Flash – News Flash – News Flash – News Flash

Both Cape Town and Gauteng have just confirmed that they will be activating water restrictions during 2026, and in our next brief, we will discuss how these will affect the everyday Consumer.

Please visit us at www.amanzirms.co.za/articles for more informative articles.

With thanks for input – City of Cape Town, Argus, Investec, World Wildlife Fund, Google, IAH commission & NGWA.