It is likely that the water borne disease impacts have been under-estimated in any
case. The most common waterborne disease is caused by the Norwalk Type A
virus. This usually results in a 24 hour GI infection (Diarrhoea). This morbidity is
often confused with minor food poisoning so the water borne health data is probably
understated, because it is interpreted as being derived from non-water related
sources. This would then underestimate the potential benefits of improving sewage
management by either installing sewerage systems or drain improvements, and
improving water quality and treated effluent disinfection.