Bacteriophage as an Index of Water Contamination

Because of technical difficulties of isolating pathogenic bacteria from waters (even from waters known to be contaminated fairly recently), the presence or absence of Bacterium coli in water supplies and the relative numbers of this organism if present are recognized as indications of the presence and degree of faecal pollution. This is based on the assumption that the more bacteria of intestinal origin there are in water, the more likely are pathogenic species to be amongst them. The presence of Bact. coli type I is accepted as the most delicate index of recent faecal contamination and the practical value of the ' coli test' in establishing the standards for drinking water is accepted by all those concerned with the bacteriological examination of water supplies. It must, however, be remembered that the evidence at best is circumstantial and conclusions drawn from it cannot be considered as unequivocal as conclusions based on direct evidence.. Further the usual method of bacteriological examination of water gives no indication whatever of the source of any contaminating bacilli found in it. They may be from animals other than man. In addition there are many problems, connected with the multiplication of . coliform bacilli which may cause difficulties in the bacteriological examination of water supplies perhaps of great significance under tropical conditions. In order to collect more direct evidence of the presence in water of contamination with excreta of human origin, a search was made for