Lost opportunity: Researcher Teboho Mofokeng says using drinking water to flush toilets is irrational.
Every day, South Africa’s coastal cities discharge roughly 300 million litres of wastewater into the sea.
For Teboho Mofokeng, a water engineering lecturer and PhD candidate at the University of Cape Town researching water management and reuse, this is a lost opportunity.
She said that amount of water is enough to provide about 1.5 million to two million people with drinking water every day “and that is just from us flushing our toilets into the sea. Surely we can rethink what we are doing.”
Mofokeng is the co-author of a new study by researchers at the university who explored using seawater to flush toilets in Cape Town.
The research, commissioned by the Water Research Commission, found that Capetonians were willing to pay up to 10% more on their water bills to use seawater to flush their toilets — as long as it doesn’t smell or stain the bowls.
Mofokeng said water could also be treated to remove harmful bacteria and reused to flush toilets. But this would require a closed water system.
In Cape Town alone, 20% to 30% of the city’s drinkable water provided to households is used to flush toilets. As the demand for housing grows, so does the need for water and sanitation.
When new housing developments are connected to the water supply network, alternatives such as seawater and recycled water for toilets should be considered, rather than using potable water.
For their study, the researchers asked 239 people whether they would be willing to flush with seawater or recycled water — or continue to flush with drinking water but pay more to do so.
They were also asked how they felt about toilet wastewater being discharged into the sea.
The respondents had mixed findings. “Overall, 90% of people were willing to move away from using drinking water for toilet flushing, but only if the new water source did not stain the toilet bowl, was clear and had no smell.”
Nearly 60% of the respondents preferred using seawater to recycled water to flush toilets.
But there were differences in preference according to income, gender and household size.
About 45% of the people interviewed earned more than R12 800 a month and they preferred to use potable water to flush toilets.
But women with a higher education qualification were more likely to pay extra for both seawater and recycled water options.
Furthermore, homes in which more than three people lived were more likely to pay for recycled water than seawater.
“My interest was in understanding whether the choices we make around using alternative water sources are embedded from a pro-environmental influence; [in other words] if I use alternative water sources, then it’s better for the environment,” said Mofokeng.
“From a research perspective, women tend to make those [environmental] choices more than men and people with a higher level of education also tend to make those kinds of decisions and also older people,” she said.
On average, 10% to 15% of Capetonians’ municipal bills went towards paying for water.
The study looked at the preferences of households that pay R350 to R900 a month for water and found they were willing to pay 5% to 10% more to use alternative water.
“In the way that we set up this experiment and the models that we are using, it allows us to understand what qualities are important for people and under what circumstances would they accept the alternative water source. It’s very clear that it has to be at a discount — and there’s high sensitivities to the colouring of the water.”
But the study found that people were not willing to foot the bill for treating wastewater that would be discharged into the sea.
They were also in favour of the city treating wastewater, but only if it reduced their water bill by up to 7%.
Mofokeng said flushing toilets with seawater has its downsides.
“It would need a duplicate network to be set up, with one network of water pipes for the drinking water supply and another for the toilet flushing water supply. This would mean that both new and ageing water systems would be set up or replaced by systems with a duplicate pipe network.
“Usually water supply networks use concrete, steel or plastic pipes. But because seawater corrodes, plastic pipes will be needed for the seawater flushing pipe network. Plastic manufacturing and the raw materials needed have a significant impact on the environment,” Mofokeng explained.
But steel or concrete pipes would need to be replaced more frequently than plastic pipes. Storage facilities, such as reservoirs, would also need to be built and a new system set up to treat seawater before it is piped to people’s homes.
The chemicals and electricity required to clean the water, supply water to consumers and eventually dispose of the wastewater would bump up the costs.
And because the country’s electricity is predominantly produced through burning coal, using up more energy in a duplicate water system would increase global warming significantly. This means a renewable energy system would need to be set up.
Mofokeng added that climate change will result in a drier south-western Africa. Unpredictable rainfall and frequent droughts will mean less freshwater available for people to drink.
She said it was crucial that coastal cities such as Cape Town, whose populations are growing, invest in water supplies from “unconventional” sources.
She said people have to become more aware that not all household activities need to use potable water.
“Increasing public awareness and education about the benefits of using alternative water can help people to accept that they won’t be able to flush their toilets with clean, drinkable water for much longer.”
The need to recycle water is a “no-brainer” around the world but the problem is public perception and public acceptance of it, Mofokeng added.
She pointed out that Windhoek, the capital of Namibia, has been producing purified drinking water from its wastewater for more than 50 years, while Singapore recycles its wastewater, turning it into safe, clean potable water.
“Until we start building new developments that have two-pipe systems, where the one is dedicated just for flushing toilets [using recycled or seawater], once people have that level of experience, then maybe it will become the new normal.”