MICROBIOLOGICAL ASPECTS OF WATER-QUALITY AND HEALTH

Historically, typhoid and cholera are well-recognized waterborne infections. Advances in laboratory techniques over the past 20 years have enabled a wide range of other faecally-excreted bacteria, viruses and protozoa to be identified as causing gastrointestinal infections. Record outbreaks are referred to where some of these micro-organisms have been spread by the contamination of drinking water, either at source or during distribution. This has usually happened when the water was untreated, or where there have been failures of the disinfection process or breaches in the integrity of the distribution system. Recent waterborne outbreaks of cryptosporidiosis have underlined the importance of adequate filtration in the prevention of waterborne transmission of this protozoon, the oocysts of which are completely resistant to the levels of chlorine that can be attained in water treatment practice. An outline is given of the current processes by which pathogenic micro-organisms are excluded from drinking-water supplies; their potential deficiencies for dealing with some of the 'newer' waterborne pathogens are also discussed.