Potable water reuse: City of Cape Town must take a precautionary approach with necessary authorisations, monitoring and controls

By Leslie Petrik, Jo Barnes, Kassim Badmus and Lesley Green 11 March 2021


The City of Cape Town appears to be rushing through a plan to inject purified sewage into the city’s drinking water system. But this is a highly complex process with considerable risk to human health if not done rigorously and in line with properly researched science. Is the City putting the health of Capetonians at risk?

The term potable water reuse is a euphemism for the recovery of drinking water from sewage effluents.

Potable water reuse is a concept that has become prominent due to the water scarcity experienced in various places in our country and elsewhere. The idea is to recover the liquid fraction from sewage and purify it to drinking water standards, then distribute it via the potable water reticulation systems. This has been done in practice for several years in Beaufort West in order to augment their potable water supply.

The City of Cape Town announced on 7 March 2021 that it will be injecting water reclaimed from sewage into the City’s potable drinking water supply during the period March to May 2021, while admitting to neither having had open public participation meetings nor having received final approval from the appointed authorities.

It is estimated that there are 248,000 manufactured substances that exist on the market and only about 181 have been tested by public entities for health and environmental effects, according to the Strategic Approach to International Chemicals Management (SAICM). The SAICM aim is to see that “chemicals are used and produced in ways that lead to the minimisation of significant adverse effects on human health and the environment, using transparent science-based risk assessment procedures and science-based risk management procedures, taking into account the precautionary approach, as set out in principle 15 of the Rio Declaration on Environment and Development…”

This principle was adopted by ministers, heads of delegations and representatives of civil society and the private sector at the Dubai Declaration on International Chemicals Management in 2006. Their mission statement says: “the sound management of chemicals is essential if we are to achieve sustainable development, including the eradication of poverty and disease, the improvement of human health and the environment and the elevation and maintenance of the standard of living in countries at all levels of development”.

This is now part of our national plan for implementation of the Stockholm Convention and is pertinent to the Sustainable Development Goals, and the United Nations Environment Programme, which in September 2020 published “An Assessment Report on Issues of Concern: Chemicals and Waste Issues Posing Risks to Human Health and the Environment”.

Sewage contains a very high load of chemicals, many of which are persistent and have carcinogenic, mutagenic or toxic effects (Tijani et al, 2016; Tijani et al, 2013). Even modern water treatment processes are unable to remove these chemicals completely. Swartz et al recommended that where potable water reuse is planned, a battery of bio-assays representing different trophic levels be included in a monitoring programme including different oestrogen mimicking assays and anti-androgenic activity.

These authors cautioned that “wastewater reuse that has not been adequately treated can be a possible exposure pathway to a high number of emerging contaminants and their metabolites”. Although some chemical compounds and pharmaceuticals have a recommended acceptable daily intake, there are many with no set reference dose values or acceptable daily intakes, and the synergistic effects of daily ingestion of numerous different compounds, even in very trace amounts, are unknown.

It should also be remembered that water recovered from sewage has just recently passed through human bodies. Pathogenic organisms in wastewater are responsible for the death of about 1.45 million people annually (Pandey et al, 2014). It is very important to achieve 99.99% pathogen removal from wastewater before it is discharged into the environment or reused. The City recently reported high levels of faecal contamination of our coast which relates to discharge of poorly treated or untreated sewage effluents (City of Cape Town: “Know your coast report”, 2019).

The process of water treatment as currently practised in the Western Cape and elsewhere in our country is basically conventional. This involves mechanical removal of solid particles in the primary stages, followed by biological nutrient removal and chemical treatments in the secondary and tertiary stages respectively. The deterioration in the quality of water due to procedural anomalies such as floc breakdown or filter overloading is very common in conventionally treated wastewater. The viruses or bacteria may be adsorbed on the retained particulate matter (clarification or filtration) which aids their circumvention of further treatment.

The quantification of pathogenic organisms and safety of treated wastewater due to be discharged into the environment or reuse, can only be established through the use of indicator species such as faecal coliforms and Escherichia coli assays. For instance, Hepatitis E virus, sapovirus, rotavirus and astroviruses are well-documented pathogens that can be present even in conventionally treated water (WHO, 2011). The relationship between E. coli and other pathogenic organisms is complex and no indicator organism can consistently predict that other organisms capable of causing disease will be absent in treated water.

Although the City gave an online presentation of their potable water reuse plans to the academic community on 9 and 23 February 2021, the presentation took place behind closed (online) doors on an invitation-only basis.

Acceptable reduction of pathogenic organisms is a necessary requirement for reuse of wastewater treatment plant effluent after disinfection. Pathogenic bacteria and viruses are resistant to secondary treatments such as conventional chlorination, or to alternative treatments such as UV, ozonation and chlorine dioxide. The pathogens can be transmitted via water through the faecal-oral route and are frequently found in municipal drinking waters. Their links to gastroenteritis outbreaks and a range of other human infections are well documented (Suliman et al, 2017; Courault et al, 2017).

Although the City gave an online presentation of their potable water reuse plans to the academic community on 9 and 23 February 2021, the presentation took place behind closed (online) doors on an invitation-only basis.

If the press statement by the City is based upon the academic stakeholder meeting that members of our team were part of on 9 February, it is not true for the City spokesperson to state that the academic community gave the proposal for potable reuse a high level of support or expressed confidence in the City’s plans. Their presence at the meeting did not signify academics’ approval of the City’s plans. Academics invited to the presentation hardly had time during that engagement to respond, although several did express their concerns in the short time available for discussion. At that meeting, we were instructed several times by City officials not to engage with the press. For City officials to endeavour to muzzle academics is disquieting.

Certainly, from what we had earlier been led to understand by the City, the demonstration sewage water recovery and reuse system in Faure was initially intended to discharge treated water into the Cape Flats aquifer for storage, not to reticulate it into the potable drinking water supply. Then the plan changed, and the City said the treated water would be used for industrial purposes and the irrigation of sports fields only. But, on 7 March 2021, Alderman Xanthea Limberg is on record in the Sunday Times confirming that the treated water will be injected into the potable drinking water supply in Cape Town during the months from March to May. We could be drinking this water already in the central and southern suburbs, without our knowledge or consent.

According to the City, we are supposed to be heading towards greater transparency to citizens and greater accountability on the part of the municipalities and officials representing us or who are providing the services for which we have to pay. We are obliged to pay for our municipal services, but in the absence of standards or with standards that do not set the appropriate limitations, have no clarity on the quality of the product water for which payment is demanded. We could unwittingly be paying for the long-term injury to our own health.

Although there was a Water Research Commission survey that purportedly found a 48.5% acceptance of the concept of potable water reuse during a time of drought, that still means that the majority of people polled were not in agreement. It is not clear whether this was polled in the area designated to receive this water. People who live in the area receiving water directly from the Faure plant are apparently unaware of any such poll. And those who were polled understood that this would be an emergency measure during serious drought conditions, not a standard daily practice to augment drinking water during times when there is no scarcity, such as the current time.

In principle, potable water reuse is a workable idea, BUT with several big provisos which need to be adequately addressed. 

The foremost issue is that our drinking water standards as well as standards for acceptable effluent are woefully inadequate to be used to determine the safety of water recovered from effluents for drinking purposes. The current water quality standards only set maxima for a few criteria in the water, such as bacteria and toxic metals. Other than E. Coli and enterococcus sp, no pathogenic organisms are mentioned. The limits for persistent organic pollutants (POPs) are completely lacking in our guidelines.

Yet our studies have shown that traces of numerous persistent organic contaminants pass through even the best water recovery systems, such as at Beaufort West. The POPs that remain in treated reuse water are compounds such as perfluorinated compounds, hormones, pharmaceuticals, personal care products, antibiotics, industrial chemicals, pesticides, herbicides etc, many of which are endocrine-disrupting, with chronic carcinogenic or toxic risks.

To get an idea of the scale of the problem of the POPs content in the sewage effluents that are currently being discharged into the peninsular environment, we have measured these compounds in seawater and effluent discharges, and have determined their bioaccumulative potential and risks in a variety of organisms (Ojemaye et al, 2020a and b; Ojemaye and Petrik, 2019; Petrik et al, 2017). Our studies show that even when background water concentrations of these chemicals are less than a nanogram per litre in seawater, these compounds bioaccumulate up to a thousandfold or more in living organisms, such as fish (Ojemaye and Petrik, 2019) and benthic organisms (Ojemaye et al, 2020a and b; Petrik et al, 2017).

Moreover, we have found a plethora of these compounds bioaccumulated in each single organism we tested. Pharmaceuticals and other persistent organic compounds are globally found in the marine environment due to sewage and other effluent discharges and our city should take note of this problem (Ojemaye and Petrik, 2019; Tijani et al, 2013), yet has rather chosen to denigrate our research (Colenbrander et al, 2021).  The synergistic impacts upon living organisms of this toxic cocktail of chemicals in the water are unknown.

Essentially, there is nothing to prevent the City of Cape Town claiming that the water meets the drinking water specifications, despite there being no hard evidence presented that they have adequately removed these compounds from the potable reuse water they wish to distribute to the City. For this reason, it is extremely worrying that no SA drinking water standards specify limits in drinking water for POPs. To date, we have not seen the stringent criteria supposedly being used by the City to qualify the potable reuse water as being safe for human consumption.

The City also has not yet transparently shown the means by which independent monitoring will be undertaken to ensure that they remain compliant to much more stringent water quality guidelines than the current drinking water standards. It is a serious concern that the City seems to plan on being its own monitoring authority. That approach, globally, will inevitably fail at crucial times.

So, the questions remain, what exactly is the City’s contingency plan in case of breakthrough contamination? How much breakthrough will be deemed safe enough, and who decides? If there is external monitoring, how often will this be done, how will it be funded, who will be appointed to police the system, and what happens when a breakthrough event is detected?

Of concern is the fact that the demonstration plant and future full capacity plant aim to inject the water directly into the water reticulation system. To our knowledge, there are no plans for a bulk holding tank facility in which treated water is retained for a period until tested adequately for safety before its consumption. It is of concern that the City has not adequately demonstrated the system’s buffering or holding capacity nor the critical control points to check water safety prior to release, nor indicated what would be the maximum criteria for qualifying the water as safe.

The City seems to rely upon diluting out any harmful substances, but that is a very risky approach. If the aim is to prepare five million litres of water for reticulation per day, that speaks of the need for a very large bulk storage capacity as a safety buffer, while quality tests are done. It is simply not feasible to withhold such a large volume of water until tests are returned, unless a dam is built, which is unlikely.

No system is perfect, and breakthrough happens, even in the best of systems. This may be due to leakages past incompetent barriers, or catastrophic failures. At a minimum, the water should not be released to consumers until it passes a rigorous 48hour toxicity screening. In practice, it takes considerably longer than 48 hours to actually quantify and identify the numerous chemicals of concern that may escape past checks in the system, in the event that these systemic safety barriers should fail. We do not know of any external laboratory that has a turnaround time of less than two weeks for such rigorous chemical testing, which testing would need to be done on a daily (if not hourly) basis. Thus, product water should be bulked for between 48 hours and about two weeks prior to qualifying for release.

So, the questions remain, what exactly is the City’s contingency plan in case of breakthrough contamination? How much breakthrough will be deemed safe enough, and who decides? If there is external monitoring, how often will this be done, how will it be funded, who will be appointed to police the system, and what happens when a breakthrough event is detected?

From a chemistry point of view, not an engineering perspective, it is known that advanced oxidation can be utilised to degrade the chemicals of concern down to their constituent parts by using free radicals that initiate and sustain the oxidation process, and the free radical generation capacity of any advanced oxidation system can be measured accurately (Mouele et al, 2020; Mouele et al, 2018; Tijani et al, 2017; Nyamukamba et al, 2017; Badmus et al, 2016; Mouele et al, 2015).

Advanced oxidation works more efficiently in combined systems to degrade persistent contaminants but it is a very exacting process and requires careful control and monitoring. This is because many compounds degrade into a plethora of unknown secondary compounds that may be more toxic than the parent compound but that cannot be identified.  Single advanced oxidation systems such as UV light or ozone, in particular, are prone to only partially degrade persistent compounds.

Moreover, the active free radicals generated by the advanced oxidation system are easily scavenged and rendered ineffective in solutions of high ionic strengths (Tijani et al, 2014; Badmus et al, 2020; Makene et al, 2019; Badmus et al, 2018; Ayanda et al, 2018). There are efficient advanced oxidation systems available on the market, but up to now the City’s engineers have not considered recent technological advances in designing their treatment train, but have elected to rely on ozonation, adsorption, and UV light.

The City’s demonstration unit has added activated carbon as the main barrier, hoping to remove the POPs via adsorption, but many compounds only adsorb on to activated carbon and other adsorbents at a particular pH, and would otherwise escape and pass through the system (Ayanda et al, 2015; Ayanda et al, 2014). Moreover, unless regularly regenerated or replenished, these adsorbents become fouled up and then would allow breakthrough. After use, they present a disposal hazard that has not been addressed.

There are too many outstanding issues for this demonstration plant at Faure to be injecting water into the reticulation system at this early stage. These issues range from lack of authorisation to inadequate or missing public participation, limited, lax or unspecified quality control criteria for measuring parameters of concern, a significant number of unresolved technical issues, ignorance of the requisite chemistry, as well as general short-sighted planning and design. The current pilot demonstration is still in its infancy, and it lacks adequate barriers, fail-safe controls, and independent monitoring. It behoves officials and engineers involved to adopt a precautionary approach and not distribute the product water to an unsuspecting public until all the necessary authorisations, monitoring and controls are in place. 

On Monday, 8 March 2021, at the 46th Session of the Human Rights Council, 15 United Nations agencies presented a joint statement that noted “rights of present and future generations depend on a healthy environment. … We have come together under the UN Secretary-General’s Call to Action for Human Rights, through the inspiration provided by the Council, and in response to the urgent call for action from all corners of the world to declare that the time for global recognition, implementation, and protection of the human right to a safe, clean, healthy and sustainable environment is now. We stand ready to support Member States in achieving this objective.”

Will the City of Cape Town follow the lead of the United Nations? Or will it fail to do so, and continue to deny the presence of persistent organic pollutants and chemicals of emerging concern in its sewage and the associated risk implications on recovered water?

The key here is that consistently the City of Cape Town has chosen to use bureaucratic mandates to contest scientific findings. The UN Statement is a call to countries, and to cities, to exercise leadership in addressing chemical contaminants of every kind. DM

Leslie Petrik is Senior Professor in the Department of Chemistry at the University of the Western Cape and is an award-winning, rated scientist and leading expert in the field of material science, as well as environmental monitoring and remediation, including wastewater treatment and beneficiation of industrial wastes. Her current related research includes investigating the environmental impacts of sewage released into the marine environment.

Dr Jo Barnes is Senior Lecturer Emeritus in the Faculty of Medicine and Health Sciences, Stellenbosch University, with specialities in Epidemiology, Research Design and Water-related Health as well as Disaster Management. She is an epidemiologist with over 35 years of experience within the health sector. Her research has predominantly focused on Community and Environmental Health, in particular, exploring the distribution and determinants of water pollution and sanitation in urban low-income housing.

Dr Kassim Badmus is a post-doctoral fellow at the Cape Peninsula University of Technology, with a PhD in Chemistry from UWC. He is a specialist in the treatment of persistent organic pollutants in wastewater with combined advanced oxidation processes.

Lesley Green is Professor of Anthropology and Director of Environmental Humanities South at the University of Cape Town, and author of “Rock | Water | Life: Ecology and Humanities for a Decolonial South Africa” (Wits University Press).


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  • Advanced treatment to destroy the 300+ substances remaining after conventional treatment (and thus routinely discharged into the environment) is where wastewater treatment must go! A trial to put such water back into potable reticulation needs extra checks and balances – where is citizen oversight?

  • By the way, the ‘liquid fraction’ of raw sewage is 99,9%, compared to 96,5% in seawater. But what our industrial society manages to put into the other 0,1% is fearsome.


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