Total Coliform & E. coli in Drinking Water – Total Coliform Rule


Public Water Systems (PWS) are defined as entities that provide water for human consumption through pipes or other constructed conveyances to at least 15 service connections or serves an average of at least 25 people for at least 60 days a year.  PWS must comply with the Safe Drinking Water Act (SDWA) and the requirements of the National Primary Drinking Water Regulations (NPDWR) (40 CRF 141), specifically meeting the requirements stated by the Total Coliform Rule.  EPA regulations require community water systems to conduct monitoring for compliance with the drinking water standards.  In addition, regulations provide that analyses must be conducted by laboratories certified by the EPA or the States.  These regulations also establish requirements for laboratory certification.

Selected Excerpts from the Total Coliform Rule (40 CFR 141.21 (f))

  • The standard sample volume required for total coliform analysis, regardless of analytical method used, is 100 mL.
  • PWS need only determine the presence or absence of total coliforms; a determination of total coliform density is not required.
  • PWS must conduct total coliform analyses in accordance with one of the analytical methods given (including ONPG-MUG Test AKA the Autoanalysis Colilert System).
  • PWS must conduct analysis of Escherichia coli in accordance with one of the analytical methods given (including Minimal Medium ONPG-MUG Test; the Autoanalysis Colilert System is an MMO-MUG test).
  • The time from sample collection to initiation of analysis may not exceed 30 hours.
  • Systems are encouraged but not required to hold samples below 10°C during transit.

Methods cited in the TCR are found in Standard Methods for the Examination of Water and Wastewater, 18th edition (1992).


The Purpose of the Total Coliform Rule (TCR) is to monitor for the presence of microbes, specifically coliform bacteria, and to determine whether the drinking water in the distribution system of  a PWS is potentially contaminated with pathogens.  Ingestion of pathogens in drinking water may result in gastroenteritis, hepatitis, myocarditis, paralysis, acute hemorrhagic conjunctivitis, meningitis, and/or other negative health impacts.


Compliance with the Total Coliform Rule

Murray-Brown Laboratories (MBL) has obtained and intends to maintain certification for the Microbiological examination of public drinking water by the State of Colorado Department of Public Health and Environment (CDPHE) using the MMO-MUG Colilert Method for the detection of Total Coliform & E. coli.

The Colilert method meets the requirements for the detection of Total Coliforms and E. coli in public drinking water as stated in the Environmental Protection Agency (EPA) Manual for the Certification of Laboratories Analyzing Drinking Water, 5th Edition (2005).

By complying with the provisions set out in the cited EPA manual, MBL is approved to perform Total Coliform & E. coli detection via Colilert in public drinking water compliance samples collected and submitted by Public Water Systems (PWS) in their efforts to satisfy the requirements of the Total Coliform Rule (TCR) and the Ground Water Rule (GWR) under the Safe Drinking Water Act (SDWA).

In order to be eligible to analyze compliance samples under the SDWA, MBL must meet the minimum criteria specified in the cited EPA manual, which includes passing an on-site audit at least once every three years, and satisfactorily analyzing a set of PT samples annually.


Many different pathogens may be present in water.  It is not practical to test for them individually.  Instead the monitoring for indicator organisms is relied on.  The indicator organisms used are total coliforms, and Escherichia coli (E. coli).  Total coliforms are a group of closely related bacteria that are generally harmless.  They are natural and common inhabitants of the soil and ambient waters (such as lakes and rivers).  They are usually not found in ground water that is free of surface water or fecal contaminates.  Total coliforms are inactivated by treatment or die off naturally in a manner similar to most bacterial pathogens and many viral pathogens.

Therefore, if total coliforms are found in the distribution system, pathogens could also be present.

Drinking water contamination can occur either before or after treatment.  Treated water may be contaminated through improperly treated or maintained facilities or in the distribution system (i.e. cross connection, aging infrastructure, leaking septic tanks, etc.).

When total coliforms are present, the system is vulnerable to pathogens, whether pathogens are actually present or not.  Total coliform testing is relatively inexpensive and easy. Fecal coliforms are a subset of total coliforms.  E. coli is a subset of fecal coliforms.  Fecal coliforms and E. coli are good indicators of fresh fecal contamination and of the potential presence of waterborne pathogens associated with fecal contamination.  Certain strains of E. coli are themselves pathogenic.

TCR compliance samples are collected in the distribution system.  There are four types of TCR compliance samples:

  • Routine:  The number of required samples is based on the population served.
  • Repeat:  These are samples that are collected in response to any routine Total Coliform (TC) positive sample.  Four samples must be collected on the same distribution system line (i.e. water main) as the original TC positive sample:  one repeat sample from the original TC positive site, at least one repeat sample at a tap within 5 service connections upstream and at least one repeat sample at a tap within 5 service connections downstream of the original sampling site; the fourth repeat sample may be collected anywhere in the distribution system to help locate any possible sources of contamination.
  • Increased Routine:  These are samples that are required the month following a routine TC positive sample.  The PWS must collect at least five routine samples during the next month following a TC positive sample.
  • Special Purpose:  samples that are taken to determine whether disinfection practices are sufficient following distribution system repair/replacement activities or samples that are collected in response to customer requests that are NOT representative of water quality in the distribution system.

Maximum Contaminate Levels (MCLs) for PWS

Acute MCL

A total coliform or E. coli positive routine sample followed by an E. coli positive repeat sample.

This creates an acute violation of the MCL and the PWS must:

  1. Notify the state by the end of the day the PWS is notified.
  2. Notify the public within 24 hours by TV, radio, hand deliver, or other State approved method.
  3. Consider advising customers of the PWS to boil their water.

Monthly MCL

A less serious but still significant potential health risk exists if more than one sample (routine and/or repeat) in a month is total coliform positive.  This creates a monthly MCL violation.  After notification by the laboratory, the PWS must:

  1. Notify the State by the end of the next business day.
  2. Notify the public within 30 days by mail, hand delivery, or other State approved method.

If a routine sample tests positive for the presence of total coliforms the PWS must:

  1. Immediately collect a set of repeat samples per positive routine sample to assess the extent of the problem;
  2. Collect 5 routine samples the next month.
  3. For every total coliform-positive sample, a set of repeat samples must be collected within 24 hours of the PWS being notified of the positive result by the laboratory.
  4. In the month following detection of total coliforms in any routine or repeat sample, the PWS must collect five routine samples.


Repeat Samples

Repeat Sample Locations

One of the repeat samples must be collected from the original sample site; 1 within 5 service connections upstream; 1 within 5 service connections downstream; and for systems serving 25-1,000 persons, and therefore only collecting 1 routine sample per month or fewer, a fourth repeat sample is required and should be collected from wherever the system believes it would best help identify the source or area of contamination.

The main reason for this repeat sampling is to determine whether the contamination is in the plumbing of an individual building or in the distribution system itself.  If a repeat sample is total coliform-positive at the same service connection, but negative at upstream and downstream service connections, the State may investigate to determine if it is appropriate to waive the total coliform-positive sample as being a plumbing system problem in the individual building.


NEXT Resource:  The Ground Water Rule (GWR)