Water Examinations by Membrane Filter and Most Probable Number Procedures

Abstract

The results of 1706 water samples examined simultaneously by the membrane filter and Standard Methods MPN procedures are reported. This study was carried out during the year July 1, 1952 to June 30, 1953 under the joint auspices of the American Public Health Association, the American Water Works Association and the Environmental Health Center, Public Health Service. The sanitation laboratory services of 8 state and one city Board of Health participated. The results of the 2 methods are compared on the basis of the 95% confidence limits of the confirmed MPN. Results of 1260 (73.8%) of the 1706 are in agreement. Of 650 samples having a coliform content in the range associated with potable waters, 571 (88%) show results in agreement by the 2 tests. These results indicate that the 2 procedures do not measure precisely the same group of organisms and that the sanitary significance of the differences in the results of the procedures is yet to be detd.