The quality of the essential commodity water is being compromised by contaminants originating from anthropogenic sources, industrial activities, and agriculture amongst others. Water scarcity and severe drought in many regions of the world also represents a significant challenge to the availability of this resource. Domestic rainwater harvesting (DRWH), which involves the collection and storage of water from rooftops and diverse surfaces, is successfully implemented worldwide as a sustainable water supplement. In South Africa, a water-scarce country, the use of domestic rainwater harvesting is predominantly practised by communities situated in KwaZulu-Natal and the Eastern Cape. While the use of DRWH tank systems can definitely suffice and serve as an alternative water supply, there is a health risk associated with the use of this water source for drinking purposes, especially if the water is used untreated. Currently the information available on the microbial and chemical quality of harvested rainwater in South Africa is limited.
To broaden the knowledge of the quality of harvested rainwater in South Africa a study was conducted by the Microbiology Department, Stellenbosch University (funded by the Water Research Commission), in Kleinmond in the Western Cape. The Kleinmond Housing Project, an initiative of the Council of Scientific and Industrial Research (CSIR), together with the Department of Science and Technology (DST), consists of 411 houses, each fitted with alternative technologies including a rainwater harvesting tank. The chemical and microbial quality of rainwater collected from the tanks of 29 houses was investigated from March until August 2012. In addition, 68 households were interviewed, by the Sociology Department, to investigate the acceptance and perception on the use of the domestic rainwater harvesting tanks.
The results obtained for the chemical analysis section for the 29 rainwater tanks in the Kleinmond Housing Scheme indicated that the rainwater quality was within potable chemical standards. Metals, cations and anions that were analysed for in the harvested rainwater samples, were all below the recommended drinking water guidelines according to the Department of Water Affairs and Forestry (DWAF), the South African National Standards (SANS) and the Australian drinking water government guidelines (ADWG). However, the microbial analysis showed that the presence of the following groups of indicator microorganisms; total coliforms, enterococci, faecal coliforms and heterotrophic bacteria, exceeded the recommended drinking water guidelines. With the use of molecular techniques, the presence of opportunistic pathogens and human pathogenic microorganisms such as, Escherichia coli, Yersinia spp., Aeromonas hydrophila,Klebsiella pneumoniae, Shigella spp. and Salmonella spp. and the protozoan spp. such as Cryptosporidium parvum, were also detected in the harvested rainwater samples.
While the chemical quality of the rainwater was generally lower than the stipulated drinking water guidelines, overall the microbial analysis indicated that the water in the domestic rainwater harvesting tanks in the Kleinmond Housing Scheme should not be used for potable and certain domestic purposes. Prior treatment of the rainwater is therefore required before the water source can be utilised for drinking purposes. First flush diverters could be installed between the roof and the rainwater tank inlet to divert large amounts of debris which accumulates on the roof surfaces. This simple intervention could potentially significantly improve the microbial quality of the harvested rainwater. A study by the Microbiology Department is also currently being conducted to improve the microbial quality of harvested rainwater, to within potable standards, through the implementation of point of use treatment technologies, such as filter systems or solar disinfection systems.
In addition, results from the Sociology investigation indicated that the community members in Kleinmond generally utilise the harvested rainwater for washing clothes and for general domestic purposes, such as cleaning inside and outside their houses. The DRWH tank users surveyed also expressed their willingness to become involved in training sessions which allow them to obtain knowledge on the operation and maintenance of the tank systems. Their willingness to participate in the training programme indicates a sense of ownership and also suggests a high level of acceptance of DRWH in the Kleinmond community.