Fecal Coliform/Fecal Streptococci Ratios in Water

Fecal Coliform/Fecal Streptococci Ratios in Water

To assist in differentiating between animal and human fecal pollution, the fecal coliform/fecal streptococci ratio (FC/FS) may be a very useful tool and much more economical than complex physiological tests on isolated bacteria.

The FC/FS ratio is based upon the generality that humans contain higher numbers of coliform in their intestines than streptococci while animals maintain higher numbers of fecal streptococci than fecal coliform.

It should be noted here that the FC/FS ratio may change as any one form of fecal pollution travels downstream. The following table may be used as an interpretive aid when evaluating water samples.

FC/FS Ratio Interpretation
4 Indicates pollution derived from human waste
1 to 2 Represents a gray area of uncertain interpretation
0.7 Indicates pollution derived from livestock, poultry or wildlife

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