Persistence of Viable Bacteria in Solar Pasteurised Harvested Rainwater


The aim of the current study was to provide insight into the viable bacterial community that persists in rainwater after solar pasteurisation (SOPAS). Unpasteurised rainwater (n = 8) was collected directly from the rainwater tank, while SOPAS-treated rainwater (n = 8) was collected from the Phungamanzi™ system (connected to the tank) at the temperature ranges of 70 to 79 °C, 80 to 89 °C, and 90 °C and above. Culturable bacteria were isolated and identified using universal 16S ribosmonal ribonucleic acid (rRNA) PCR. Results indicated that Klebsiella spp., Pseudomonas spp., Enterococcus spp. and Bacillus spp. were present in untreated rainwater and sporadically persisted in the SOPAS samples collected at the different temperature ranges. Pseudomonas spp. and Bacillus spp. were the only genera found to persist up to a temperature of 98 °C. Genus-specific polymerase chain reaction (PCR) of total genomic deoxyribonucleic acid (DNA) extracted from the rainwater samples indicated that the most frequently detected genera present after SOPAS were Klebsiella (87.5%) and Pseudomonas (62.5%). The quantification of viable Klebsiella was performed using ethidium monoazide bromide quantitative PCR (EMA-qPCR), which revealed that intact Klebsiella cells persisted up to 98 °C with 9.3 × 104 gene copies mL−1 recorded. While intact Pseudomonas and Legionella cells have been detected in SOPAS-treated rainwater (> 90 °C), this study confirmed that Klebsiella and Bacillus are also viable at temperatures above 90 °C and may potentially result in health risks associated with the utilisation of SOPAS rainwater. Secondary or combination treatment procedures are thus required to effectively reduce the level of these persisting viable opportunistic pathogens.

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The authors would like to thank Jacques de Villiers from the Crest Organisation (Somerset West, Western Cape) for providing the Phungamanzi™ system.


The Water Research Commission (WRC K5/2368//3) and the National Research Foundation of South Africa (grant number 90320) funded this project. Opinions expressed and conclusions arrived at are those of the authors and are not necessarily to be attributed to the National Research Foundation.

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Clements, T., Reyneke, B., Strauss, A. et al. Persistence of Viable Bacteria in Solar Pasteurised Harvested Rainwater. Water Air Soil Pollut 230, 130 (2019).

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  • Roof-harvested rainwater
  • Solar pasteurisation
  • Bacillus
  • Klebsiella
  • EMA-qPCR