Escherichia coli: the best biological drinking water indicator for public health protection

Public health protection requires an indicator of fecal pollution. It is no t necessary to analyse drinking water for all pathogens. Escherichia coli i s found in all mammal faeces at concentrations of 10 log 9(-1), but it does not multiply appreciably in the environment. In the 1890s, it was chosen a s the biological indicator of water treatment safety. Because of method def iciencies, E. coli surrogates such as the 'fecal coliform' and total colifo rms tests were developed and became part of drinking water regulations. Wit h the advent of the Defined Substrate Technology in the late 1980s, it beca me possible to analyse drinking water directly for E. coli (and, simultaneo usly, total coliforms) inexpensively and simply. Accordingly, E. coli was r e-inserted in the drinking water regulations. E. roll survives in drinking water for between 4 and 12 weeks, depending on environmental conditions (te mperature, microflora, etc.). Bacteria and viruses are approximately equall y oxidant-sensitive, but parasites are less so. Under the conditions in dis tribution systems, E. coli will be much more long-lived. Therefore, under m ost circumstances it is possible to design a monitoring program that permit s public health protection at a modest cost. Drinking water regulations cur rently require infrequent monitoring which may nor adequately detect interm ittent contamination events; however, it is cost-effective to markedly incr ease testing with E. coli to better protect the public's health. Comparison with other practical candidate fecal indicators shows that E. coli is far superior overall.