A borehole located in Port Harcourt, Rivers State, Nigeria, drilled to a depth of 55 m, was analysed for its water quality between May and September 2001. All the physicochemical parameters analysed were within the limits stipulated by the World Health Organization (WHO) with the exception of pH, which fell within the range 4.98–5.15. Bacteriological analysis indicated a low count of total coliforms (3 cfu 100 ml−1), faecal coliforms (0 cfu ml−1) and heterotrophic bacteria (159 cfu ml−1). The presence of Chromobacterium violaceum, a pathogen known to cause chromobacteriosis in humans, was detected in the heterotrophic plate count (3 cfu ml−1). Other pathogenic organisms, as indicated in the WHO guidelines for water quality, were not detected. Repeated analysis in July indicated a low heterotrophic count (180 cfu ml−1) with 5 cfu ml−1Chromobacterium violaceum. Total coliforms and faecal coliforms were higher (45 cfu 100 ml−1 and 12 cfu 100 ml−1, respectively). Other pathogenic organisms were not detected. Analysis of samples collected in September indicated a high level of heterotrophic bacteria (700 cfu ml−1) while total coliforms and faecal coliforms were too numerous to count. The persistent occurrence of Chromobacterium violaceum in this borehole is a cause for concern. There is need for more research on the occurrence of Chromobacterium violaceum in drinking water sources and the epidemiology of its associated disease so that it can be included on the list of waterborne pathogens by WHO and the US Environmental Protection Agency (EPA).

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