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Harvested Rainwater Harbors Pathogens

South Africa has been financing domestic rainwater harvesting tanks in informal low-income settlements and rural areas in five of that nation’s nine provinces. But pathogens inhabit such harvested rainwater, potentially posing a public health hazard, especially for children and immunocompromised individuals, according to a team from the University of Stellenbosch. The research was published ahead of print in Applied and Environmental Microbiology.

International studies had indicated that harvested rainwater frequently harbors pathogens, and that, in light of the financing of harvesting tanks, drove the investigators to study the matter locally, says principal investigator Wesaal Khan.

The sampling was conducted in the Kleinmond Housing Scheme, which was initiated by the South African Council for Scientific and Industrial Research and the Department of Science and Technology. The houses, designed to be sustainable, are approximately 400 square feet, with alternative technologies such as solar panels and the rainwater tanks.

The list of predatory prokaryotes the investigators found includes Legionella (found in 73 percent of samples), Klebsiella (47 percent) Pseudomonas (19 percent of samples), Yersinia (28 percent), Shigella (27 percent), and others. They also found some protozoan parasites, including Giardia (25 percent of samples).

Many of the pathogens are normal fresh water inhabitants, but Salmonella (6 percent of samples) indicates human fecal contamination, while Yersinia are markers of fecal contamination by wild and domestic animals, according to the report.

Residents, many of whom are little-educated and unemployed, typically use the rainwater for washing clothes and house-cleaning, but about one quarter of people polled in the study said they used it for drinking, as well. The finding that coliforms and Escherichia coli counts from rainwater samples—markers of fecal contamination—always significantly exceeded drinking water guidelines, reinforces the World Health Organization’s opinion that rainwater must be pretreated prior to use for drinking, says Khan.

Rainwater harvesting is needed in South Africa’s “informal communities” because residents often depend on communal “standpipe” systems that frequently serve more than 100 people, who may have to walk as far as a third of a mile to get water, says Khan. Approximately 23,000 rainwater tanks have been installed, two-thirds of them in the Eastern Cape and one-third in KwaZulu Natal. Nearly 20 percent of South Africans lack sustainable access to water.

Source: American Society for Microbiology (ASM)


These rainwater harvesting installations do not use the Aquarista rainwater system that filters the water before it enters the tank. Filtering the water before it enters the tank removes leaver and debris that wash off from the roof. Should such leaves and debris enter the tank it can be expected the pathogens breed in the water. See note below.

Aquarista never specifies rainwater as potable for the very reason that there may be unexpected animal (or human – as alluded to above) matter landing on the roofs of homes. We do however have a filtering system that filters the water down to 5 micron and than steralises that water.

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“There were no obstacles obstructing the roofs, i.e., trees or electrical power lines, and no first flush diverters were installed to eliminate the first flush of debris from the roof surface into the tanks.”


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