Microbiological quality of drinking water at eight water treatment plants

Eight drinking water treatment plants were sampled monthly during one year to evaluate the removal of bacterial indicators, new indicators and some pathogenic bacteria. Six plants are allocated along the Nile River at Cairo segment and the two others on Ismailia Canal. In this study many parameters were determined; the classical bacterial indicators (total bacterial counts at 22 and 37 degreesC, total coliforms, faecal coliforms and faecal streptococci) show the same trend in all plant intakes except faecal streptococci parameter. The numbers of faecal streptococci in plant intakes on the main stream of Nile River ranged from 8 to 250 MPN/100 ml, but the others ranged from 80 to 2700 MPN/100 ml. With regard to new indicators; total yeasts, Candida albicans, Aeromonas hydrophlia and total staphylococci ranged from 10(1) to 10(5), 10(2) to 10(5), 10(2) to 10(5) and 10(2) to 10(3) cfu/100 ml, respectively. In case of pathogens, salmonellae ranged between 10(2) and 10(3) cfu/100 ml, total vibrios varied between 10(2) and 10(4) and the Listeria group ranged from 10(2) to 10(5) cfu/100 ml from the intake samples. All tested samples from the outlet of water treatment plants, which produce drinking water, were free of classical bacterial indicators. So the produced water has a good quality from the bacteriological point, according to national and international regulations. On the other hand, the drinking water from some tested plants had one or more positive parameters of new indicators and pathogenic bacteria.