The efficiency of a low-cost hydrogen sulphide (H2S) kit as an early warning test for assessing microbial rainwater quality and its correlation with standard indicators microorganisms

Abstract

Testing microbial quality of the harvested rainwater remains a challenge in many countries. The H₂S test kit is a low-cost microbiological field-based test which can be used in areas where water testing facilities are limited. This study compares its efficiency with the standard indicators microorganisms in the detection of faecal contamination of rainwater in South Africa. A total of 88 rainwater samples were collected from various tanks in the Eastern Cape, South Africa over three months in 2016. The collected samples were analysed for faecal bacterial contamination using the H₂S test kit, Colilert-18/Quanti-tray^®/2000 and the membrane filtration technique for faecal coliforms (MFT). The correspondence rate of the H₂S test kit with MFT was 88 %, while for the Colilert^® it was 76 %. The H₂S test kit confirmed faecal contamination when concentrations of standards indicators microorganisms were 5 most-probable number of cells/100 cm³ or higher. Overall, the best correspondence of the H₂S test kit with Colilert^® was observed at E. coli concentrations above 50 most-probable number of cells/100 cm³. Results of the H₂S test kit correlated better with MTF, while the medium used has strongly influenced the enumeration of faecal contamination. Results point to strong effect of media used and revealed the need to calibrate the correspondence between the standard indicator microorganisms and the H₂S test kit under local conditions for specific settings.