H2S paper strip method - A bacteriological test for faecal coliforms in drinking water at various temperatures

Water-borne diseases are a major health problem in many countries. Faecal contamination of drinking water is one of the main cause of these disease outbreaks as many pathogens are carried through human faeces. At present the quality of drinking water is ensured by testing the water sample for total coliforms and thermotolerant coliforms of E. coli. However when applied in remote areas the standard methods have various limitations. The distance to laboratory facilities and the high cost of analysis restrict water quality assessment in remote areas and in developing countries. Under such circumstances an on-site bacteriological test is considered to be highly essential for routine water quality testing, The H2S paper Strip Method has been developed as a quick, inexpensive and easy to use method to test drinking water for remote and rural areas. With this method H2S producing bacteria cause water sample to turn black when faecal contamination is present. The present work analyses the reliability of the H2S method for detecting faecal contamination of water samples. A faecal sample of a healthy person was used for the study in order to get a well balanced microbial population. The minimum concentration of faecal coliforms in a 100 ml sample that could be detected by this method as well as the incubation period required at various levels of faecal contamination were studied. The range of temperatures at which the method was effective and the incubation period required at various temperatures were also determined. The bacterial count in serial dilutions of the water sample was estimated by m-FC agar plates. The H2S method was found to be able to detect the contamination level down to 1 CFU of faecal coliform in a 100 ml sample. Although the H2S method could be used at a temperature range of 14 to 44°C, temperatures between 28 to 37°C gave faster results. An incubation period of only 24 hours was required at 37°C which was found to be the most suitable incubation temperature. The incubation period increased with a decrease or increase in temperature. It was concluded that a temperature ranging from 28 to 37°C could be recommended for the H2S method. Over this temperature range the concentration of faecal coliforms also had no influence on the incubation period