Professor Timothy Dube conducted a study on the use of greywater in gardens and found the issue wasn’t the water but the public perception which he hopes will change.
Cape Town, South Africa (07 July 2022) – Ever since the threat of Dazy Zero in the Western Cape, Capetonians have come up with ways to be water savvy. That said, many were nervous about using greywater to water food gardens, in case it contained contaminants. With so many neighbouring provinces experiencing some form of drought, greywater is more essential than ever!
The University of Western Cape has been running studies on greywater usage on food gardens and come up with a report that many gardeners would be keen to read.
What is greywater? Greywater refers to water that is collected from sources of household water that are not used for waste purposes. These sources include, sinks, baths, showers, washing machines and dishwashers.
As many of these sources of greywater would contain detergents such as soap, dishwashing liquid and washing powder; many gardeners have been reluctant to use the water sources on their food crops. With both water and food scarcity prevalent problems in Southern Africa, the studies managed by Professor Timothy Dube from UWC, on the safety of greywater have been essential.
Prof Dube shared that through research done in the Western Cape and Limpopo, they have been able to measure the types of greywater and conclude it is safe to use. The biggest issue he found was not the water but the perception of the water.
“There’s a big problem, though: consumers fear that greywater isn’t safe for use on domestic gardens. Alongside colleagues, I have conducted several studies to understand this reluctance. In two of these studies, in South Africa’s Limpopo province, we found that people believed household detergents from greywater shouldn’t be used on food gardens. We also examined the quality of greywater being used in these areas – and found that it is, by and large, safe for domestic irrigation.”
The science behind these studies on a global scale is outstanding. It has been shown through studies in the United States, that greywater used for flushing toilets or in food gardens helps reduce the use of drinkable water by 30%.
Prof Dube wanted to understand why South Africans are so reluctant to use greywater as a source for crops, so a big part of the study was based on this research.
“We set out to understand what these objections are among people in the country’s Limpopo province. Limpopo 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’s 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 shouldn’t be continuously used for irrigation.”
The residents that took part in the study and used their greywater for their home crops, found they had better crop yeilds and that the plants were not being attacked as badly by usual garden pests.
“However, residents from both villages who did use greywater reported that 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 is actually in greywater used in these villages and whether it’s 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’s safe for human consumption. These ranges are set out in the World Health Organization’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 that 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’s 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.”
Prof Dube believes that policies should be implemented to aid South Africans in installing greywater systems. These systems will go a long way to providing food and water security for substance farmers and home growers.
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