Indicator Systems for Assessment of the Virological Safety of Treated Drinking Water

Abstract

Conventional methods cannot detect the viruses of prime importance, and are too expensive, complex and slow for routine quality surveillance. Coliform bacteria generally used as indicators of virological quality, may also have shortcomings because viruses have been recovered from drinking waters which meet conventional coliform limits, and some viruses may be more resistant to certain disinfection conditions. However, the shortcomings of coliforms can be overcome by the inclusion of additional indicator organisms. Indicator systems consisting of various combinations of standard plate counts, coliphages, faecal streptococci, Pseudomonas aeruginosa, acid-fast bacteria and clostridia proved reliable and practical for surveillance of the virological safety of drinking water supplies, even those derived by the direct reclamation of wastewater. The combination of indicator systems depends on factors such as the quality of the raw water, the treatment processes, and the efficiency of operation. Despite practical and reliable features of available indicator systems, further refinement is essential. This would include analyses at higher frequency and results in less time, ideally in the form of continuous early-warning alarm systems. Equally important is technology which is within reach of the limited financial resources and expertise of those parts of the world which suffer most from waterborne diseases.