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Related Experiment Videos

Holding effects on coliform enumeration in drinking water samples.

A E McDaniels, R H Bordner, P S Gartside

    Applied and Environmental Microbiology
    |October 1, 1985
    PubMed
    Summary
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    Drinking water coliform counts decline significantly over time, even at 5°C. Storing samples for 24 hours may lead to falsely safe drinking water test results.

    Area of Science:

    • Environmental Microbiology
    • Water Quality Analysis
    • Public Health

    Background:

    • Standard drinking water analysis requires strict adherence to sample holding times and temperatures.
    • Compliance with these holding limits is mandated by the National Drinking Water Laboratory Certification Program.
    • Previous research indicated challenges in meeting these stipulated holding conditions.

    Purpose of the Study:

    • To investigate the impact of storage time and temperature on coliform and heterotrophic bacteria counts in drinking water samples.
    • To assess potential discrepancies in microbiological testing results due to deviations from standard holding protocols.
    • To determine if changes in bacterial levels during storage could lead to misclassification of water safety.

    Main Methods:

    Related Experiment Videos

  • Analysis of 17 treated water samples from a municipal system (1981) and 12 samples (1983).
  • Samples were inoculated with specific coliform strains (Enterobacter cloacae, Citrobacter freundii).
  • Samples were held at 5°C and 22°C and analyzed for coliforms (membrane filter, fermentation-tube) and heterotrophs (pour plate) at 0, 24, 30, and 48 hours.

    • Main Results:

    • Coliform counts exhibited a significant linear decline over time at both 5°C and 22°C.
    • At 22°C, E. cloacae and C. freundii levels decreased by 47% and 26% within 24 hours, respectively.
    • At 5°C, E. cloacae counts declined by 23% within 24 hours, with similar trends observed for naturally occurring coliforms.

    Conclusions:

    • Standard holding time and temperature requirements for drinking water microbiological testing may not be consistently met.
    • Coliform populations decrease significantly during storage, potentially leading to underestimation of contamination levels.
    • Water samples initially exceeding safe limits could be misclassified as satisfactory after 24-hour storage, highlighting a critical issue for public health protection.