Estimating Mean Coliform Densities of Water Distribution Systems

Current drinking water regulations set a limit on the average number of coliforms allowed in samples that are collected during distribution system monitoring. This article presents evidence that the average number of coliforms in monitoring samples is a poor estimate of the mean coliform density of the distribution system. The evidence includes variance in coliform counts, data truncation caused by limitations of the examination methods, changes in coliform densities during transport of the samples to the laboratory, and false results. A regulation based on the fraction of monitoring samples with coliform densities greater than a preselected limit may be a feasible alternative to the current microbiological maximum contaminant level.

[1]  W. Grabow,et al.  Comparison of m-Endo LES, MacConkey, and Teepol media for membrane filtration counting of total coliform bacteria in water , 1979, Applied and environmental microbiology.

[2]  R. Christian,et al.  Frequency distribution of coliforms in water distribution systems , 1983, Applied and environmental microbiology.

[3]  M. Lechevallier,et al.  Comparison of Verification Procedures for the Membrane Filter Total Coliform Technique , 1983, Applied and environmental microbiology.

[4]  Marc A. Goshko,et al.  Coliform occurrence and chlorine residual in small water distribution systems , 1983 .

[5]  J. Delfino,et al.  Underestimation of total-coliform counts by the membrane filter verification procedure , 1982, Applied and environmental microbiology.

[6]  Edwin E. Geldreich,et al.  The Necessity of Controlling Bacterial Populations in Potable Waters: Community Water Supply , 1972 .

[7]  M. Lechevallier,et al.  Failure of the most-probable-number technique to detect coliforms in drinking water and raw water supplies , 1981, Applied and environmental microbiology.

[8]  M. Lechevallier,et al.  Influence of diluents, media, and membrane filters on detection fo injured waterborne coliform bacteria , 1982, Applied and environmental microbiology.

[9]  G. McFeters,et al.  Influence of environmental stress on enumeration of indicator bacteria from natural waters. , 1975, Applied microbiology.

[10]  J. Clark.  The detection of various bacteria indicative of water pollution by a presence-absence (P-A) procedure. , 1969, Canadian journal of microbiology.

[11]  B. Olson,et al.  Coliform inhibition by bacteriocin-like substances in drinking water distribution systems , 1981, Applied and environmental microbiology.

[12]  K. E. Cox,et al.  Effect of Age and Storage Temperature on Bacteriological Water Samples. , 1949 .

[13]  Wesley O. Pipes,et al.  Frequency Distributions for Coliform Bacteria in Water , 1977 .

[14]  R. Bordner.  Microbiology: methodology and quality assurance , 1982 .

[15]  V. Cabelli,et al.  The effect of oxidase positive bacteria on total coliform density estimates. , 1977, Health laboratory science.

[16]  J. A. McCARTHY.  Storage of water samples for bacteriologic examinations. , 1957, American journal of public health and the nation's health.

[17]  B. K. Lonsane,et al.  Effect of storage temperature and time on the coliforms in water samples , 1967 .