The occurrence of faecal streptococci, as a supplement to faecal coliforms, indicates faecal pollution by warm blooded animals. Since the faecal streptococci have a limited survival time outside the animal intestine and are not capable of multiplying in the environment, their presence indicates a very recent pollution.
Moreover, certain species of faecal streptococci are often associated with particular animals. For example, S. bovis occurs mainly in sheep and cattle, S. equinus in horses and S. avium in poultry and other birds. The comparison between the number of E. coli and of faecal streptococci in water can be used to determine the precisesource of contamination.
A high ratio of E. coli to faecal streptococci suggests a human source and a ratio less than one suggests an animal source. A differential count of the actual streptococcal species present in water can help to find out the exact source of contamination.
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