SYNOPSISInJuly/August1985 a significant outbreak of giardiasis occurred in part of south Bristol. An epidemiological inquiry carried out strongly suggested that the outbreak was water‐borne. Although no positive evidence was found to link the outbreak with mains water. the Company immediately accepted its feasibility m d co‐operated fully with the Hcalth Authorities in the ensuing investigation.The piper ilescrihes the investigation to ascertain whether the supply system was involved, and considers some of the broader implications of the situat