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Coliforms were chosen as indicators of microbial contamination of water in the 1880s. Total Coliforms are considered an indicator of overall water quality and treatment efficiency.
There is no correlation between Total Coliform and human health; it is an indicator species group only.
When Total Coliform is detected in a water sample it is assumed that conditions within the water distribution system are favorable for bacterial growth, and pathogenic (disease causing) microorganisms may be present. Fecal Coliforms are a subgroup of the Total Coliform organisms.
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The North Kingstown Department of Water Supply collects samples on a weekly basis from sampling stations located throughout the water distribution system. The testing sites include all five of the system storage tanks and 13 other dedicated sampling stations.
While it is not a requirement of the Total Coliform Rule (TCR), the Water Department also collects weekly samples from the ten (10) water supply wells.
The samples are analyzed for Total Coliform Bacteria and Fecal Coliform Bacteria at a licensed laboratory.
The testing method requires that filtered samples be incubated at certain temperatures. It takes between 48 and 72 hours to receive confirmation of the presence of Total Coliform bacteria.
Presumptive results are available after 24 hours of incubation. Presumptive results are an indication that Total Coliform may be present.
It takes an additional 24 hours to determine if Fecal Coliform is present and if it is not, it may take an additional 24 hours to confirm the presence of Total Coliform.
In accordance with the Total Coliform Rule, if any routine sample tests Total Coliform positive, it must be analyzed for Fecal Coliform.
If any sample is found to be Total Coliform positive, the water system must collect a set of repeat samples for each positive sample. The repeat samples confirm the presence of Total Coliform bacteria in the distribution system.
A sample must be collected from the sampling station that had the initial positive sample and samples must also be collected from locations upstream and downstream of that sampling station. In most cases these upstream and downstream locations are kitchen or bathroom faucets in homes or businesses located around the sampling stations.
In accordance with the Total Coliform Rule, five (5) percent of a water system’s monthly samples can be Total Coliform positive.
A water system is in violation of the rule if more than five percent of its monthly samples are positive.
Such a violation requires that a public notice be advertised in the newspaper acknowledging the violation. This type of violation does not result in a boil water advisory.
If Fecal Coliform is detected in a routine sample the water system must notify the Rhode Island Department of Health within 24 hours of learning of the positive sample.
Repeat samples must be collected. If either Total Coliform or Fecal Coliform is detected in any repeat sample, the water system is in violation of the Total Coliform Rule. This type of violation is considered an acute violation and results in the issuance of a boil water advisory.
Under our current approved sampling schedule, routine samples are collected on Tuesdays. We receive the presumptive results from the laboratory at the end of the day on Wednesdays. Repeat samples are collected on Thursdays, and the confirmation of the results of the repeat sample analysis are not available until Saturday or Sunday of the same week.
Sometimes presumptive positive results do not confirm, which is why boil water advisories are not issued on presumptive results.