Western Cape: Kleinmond-harvested rainwater not fit for human consumption

The article below serves as a reminder that if rainwater from water tanks is to be used for drinking, it must be adequately purified.  Rainwater is naturally pure and probably the healthiest water to drink before it reaches the collection surface.  Once it is channelled through pipes and gutters, it can be contaminated by debris on these surfaces.  The quality of the water collection tank is important too – be sure to choose a brand of water tank that has a secure lid and has an inner black lining to prevent algae growth.

Rainwater collection tanks should have a secure lid and if the water is to be used for drinking, it must be purified/filtered.

A recent study by the Water Research Commission (WRC) has found that untreated water collected by rainwater harvesting tanks provided in a low-cost housing project in Kleinmond, in the Western Cape, did not meet drinking water standards.

The Kleinmond Housing Scheme, which comprises 410 units, was conceptualised by the Department of Science and Technology, the Western Cape Provincial Department of Human Settlements and the Overstrand local municipality in 2007.

Various technology innovations had been applied in the houses including modular masonry material, reinforced ring beams, prefabricated plumbing and a 2000 litre rainwater harvesting tank.

“While domestic rainwater harvesting has been put forward as an alternative water supply, little information is available on whether harvested rainwater is safe for human use or even how local communities feel about using the water from such an alternative source,” the WRC said on Friday.

The research team, comprising researchers from the departmentd of Microbiology and Sociology & Social Anthropology at Stellenbosch University tested the chemical and microbial quality of the rainwater collected by the tanks of 29 houses over a six-month period.

While the results obtained in the chemical analysis indicated that the rainwater quality was within potable chemical standards, with metals, cations and anions within recommended drinking water guidelines, the microbial analysis found that the presence of coliforms, eneterocci, faecal coliforms and heterophobic bacteria exceeded the recommended guidelines.

The presence of several opportunistic pathogens, such as e.coli, cryptosporidium and salmonella, were also detected.

“In short, the water from the rainwater harvesting tanks in Kleinmond is not fit for human consumption and prior treatment is required before the water source can be used for drinking purposes,” the WRC stated.

It explained that the main causes of the contamination were dirt and faeces from birds and small animals that fell into the water tank. Other sources of contamination included leaf debris and organic material that was washed into the tanks, animals and birds that fell into uncovered water tanks, as well as breeding mosquitoes.

It was also found that many households placed their garbage bags on top of the water tanks to protect them from being ripped by stray dogs. These garbage bags could easily contaminate the water, especially if the water tanks were leaking or broken or if the lid was absent.

“This general lack of awareness of contamination hazards highlights the importance of training users in the proper use and maintenance of the technology,” the WRC said.

“Rainwater tanks are not a ‘fit-and-forget’ technology and require regular maintenance and upkeep. Unfortunately, most water tank users at Kleinmond admitted that they did not know how to maintain their water tanks, although they did indicate a willingness to learn.

“Users need to ensure that their water tanks are covered to prevent mosquito breeding, as well as sunlight from reaching water, which promotes algal growth,” WRC research manager Dr Nonhlanhla Kalebaila stated.

The organisation further recommended that some form of pretreatment be installed to make the rainwater safe for human consumption and added that, as a result of this study, the Stellenbosch University team was now investigating the use of solar water pasteurisation and facilitation systems for the treatment of harvested rainwater.

However, another survey done by the Stellenbosch University indicated that the majority of the Kleinmond Housing Scheme community members instinctively steered clear of using the water from their rainwater harvesting tanks for drinking purposes.

About two-thirds of the respondents did not use the water in the tank for drinking, while the majority of those who did use it for drinking only did so 24% of the time.

Despite not using the harvesting rainwater for drinking purposes, almost all users saw the tank as being of benefit to them, particularly as it enabled them to use less municipal water. In addition, the water tanks became a convenient asset during times of municipal water disruption.

Source: Engineering News (By Leandi Kolver)

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