Early warning of faecal contamination of water: a dual mode, automated system for high- (< 1 hour) and low-levels (6-11 hours)

There is a recognised need for methods that permit rapid estimation of the sanitary quality of water e.g. during raw water monitoring and emergencies involving water treatment failure or main breaks in a distribution network. In this study, two models for predicting the level of faecal contamination of water were studied. The first format, based on measurement of beta -gal actosidase activity by the automated Colifast analyser, detected faecal con tamination of high levels, corresponding to > 15 thermotolerant coliforms ( FC)/5 mL, in 1-3 h, in a format that allowed for semi-quantification of res ults. By setting up a cut-off level, the system could be used as an operati onal tool identifying random increases in faecal contamination during routi ne raw water monitoring. A second Presence-Absence format was dependent upo n the growth of low levels of FC with subsequent detection in the Colifast analyser. 95% of water samples containing 1-15 FC/sample volume showed posi tive detection after 11 h.