SA dubious about greywater, but it’s a saviour
Some people have even found their gardens produce more food after greywater is used, and it repels insects too
After three consecutive dry winters from 2015 to 2017, “Day Zero when the taps run dry
loomed large for Cape Town and its surrounds in 2018.
Municipalities introduced a slew of water restrictions and, almost overnight, Capetonians became familiar with greywater. Many previously let this untreated water from baths, showers, kitchen sinks, washing machines and the like run down the drain. Then they installed storage tanks or used buckets of it to flush their toilets or water their lawns. It was a boom time for domestic greywater technologies.
Thanks to residents’ sparing use of water, including the adoption of greywater use, Day Zero never arrived. But there are lessons to be learnt from that experience, especially around the potential of greywater in seasons of plenty and drought.
And the dry times are not done yet. Scientists have repeatedly cautioned that climate change means water shortages remain a real risk. Gqeberha is on the verge of its own Day Zero.
The broader sub-saharan region is also threatened with dwindling water supplies and access.
Researchers have long argued that greywater has the potential to contribute to SA’S food security if it is used to water domestic food gardens.
There is a big problem though: consumers fear greywater is not safe for use on domestic gardens. With colleagues, I have conducted several studies to understand this reluctance. In two of them in Limpopo, we found people believed household detergents from greywater should not be used on food gardens.
We also examined the quality of greywater being used in these areas and found it is, by and large, safe for domestic irrigation.
Greywater is used all over the world. Studies as far afield as Los Angeles, Brazil and Malaysia have shown using greywater to flush toilets or water domestic gardens can save up to 30% of potable, drinking-quality water. It has been safely used for irrigation in contexts as diverse as Australia, Cuba, Bolivia, Jordan, Tunisia, Uganda, the UK, the US and, as I explored in one study with colleagues, Zimbabwe.
The US has used treated greywater for irrigation since 1925. In Spain, its use is becoming de rigueur: regulation requires such systems must be installed in new buildings.
But if South Africans are to embrace this important water source, their concerns must be addressed.
We set out to understand what these objections are among those in Limpopo. The province was selected as the test area because it is predominantly arid and water scarce. High temperatures, droughts and erratic rainfall contribute to crop failure and food insecurity. We also tested whether the greywater that is available for use there can be safely used on domestic gardens.
The answer is “yes, mostly”, with the caveat that any greywater containing harsh pollutant loads should not be continuously used for irrigation.
Limpopo is a largely rural province. Subsistence farming is the core of many people’s livelihoods. Frequent droughts have hampered crop production and those in the communities we studied now keep small home gardens to try to make up for lost crops in larger fields.
We asked people from two
Some people have even found their gardens produce more food after greywater is used
villages to share their perceptions about reusing greywater for home gardening.
Respondents worried about using water that contained household detergents to water their gardens. They feared their plants would die and the water would contaminate their food; some were worried the greywater may be poisonous or have unhealthy side effects.
They were especially reluctant to use greywater when running water, which they found more convenient, was readily available.
However, residents from both villages who did use greywater reported their gardens produced more food than they had before this approach was used.
Some also reported that the greywater appeared to repel some of the insects that would typically eat plants.
The second study focused on what was in the greywater used in these villages and whether it was safe for domestic irrigation. We concluded that levels of ph
— the measure of acidity and alkalinity in a substance — in untreated greywater were within widely held acceptable ranges for what is safe for human consumption.
These ranges are set out in the World Health Organisation’s water quality standards.
The sodium (salt) levels of much of the greywater we tested were also within prescribed ranges.
There are caveats, of course. Some of the water we tested contained harsh, industrial chemicals and was not suitable for irrigation.
We propose greywater is best used for home gardening when freshwater supplies fall short: it should be seen as a complement rather than a wholesale alternative to freshwater, since overusing it may negatively affect soil quality.
The use of greywater should be stopped, for example, on rainy days.
This allows for leachate, the process in which water courses through the soil and extracts soluble or suspended solids, to occur. It is a sort of cleansing and resetting of the soil.
Greywater can be used more frequently in the dry season when fresh water is less available.
This has implications for policy. The public should be encouraged — even aided — to install greywater systems in their homes.
More research on the safety of untreated and treated greywater will become essential.
Investment in technologies for the treatment of greywater should be supported.
Public education drives about its use will be necessary, too. This approach has been successful in places such as Zimbabwe, India, Uganda and Japan. – This article was first published by The Conversation.
● Timothy Dube is a professor of geospatial sciences, University of the Western Cape (UWC). This work was funded by the Council for Scientific and Industrial Research (CSIR), IBS-HCD interbursary, SA, as part of Dr Pabalelo Makgalake Radingoana’s PHD work under Prof Dube’s supervision.