ABSTRACT
All this is of more than historical interest, since in many parts of the world today waterborne diseases remain a major hazard. They are endemic in those countries which have not yet established systems for the sanitary disposal of wastes. It is striking that in times of war or natural catastrophe, when sanitary systems cannot be maintained satisfactorily, waterborne diseases take very little time to spread through the human population. Even in countries where waterborne diseases are not considered endemic, the speed and frequency of international travel and
the magnitude of international trade present a constant threat of the reintroduction and spread of infections. Further, increasing demands upon the water resources even of developed countries present new public health problems. Britain, for example, is not a country which could be considered as suffering from an overall shortage of water. Nevertheless the demands on the country’s water resources are such that it is increasingly necessary for water to be reused. The preferred sources of water supply are upland surface waters or ground water from deep wells or boreholes; these are unlikely to be contaminated with noxious chemicals or diseasecausing organisms and can be rendered suitable for potable water supply with minimal treatment. However, Evans and Johnson (1984) estimate that already 30% of Britain’s water supply is derived from lowland rivers. Such water is likely already to have been used several times over by communities upstream, and to have received waste discharges from domestic, agricultural and industrial sources. The reuse of water poses special problems in relation to the spread of infectious diseases and of other harmful effects caused by chemical contaminants.
