Coliform Bacteria

Capital Regional District Water Department
2000 ANNUAL BACTERIOLOGICAL SUMMARY OF SOOKE DISTRICT DRINKING WATER - June 29, 2001

3.1.1. TOTAL COLIFORM BACTERIA

Total coliform bacteria are a group of bacteria found in high numbers in both human and animal intestinal wastes and are therefore are found in water that has been contaminated with fecal material. Unfortunately, bacteria with the biochemical characteristics of total coliforms are also found in non-contaminated water. Thus, in the absence of fecal coliforms, the presence of total coliforms may indicate older fecal contamination or the presence of decaying organic matter. Although the total coliform bacteria group is a less reliable indicator of sewage contamination, because of its superior survival characteristics, it is preferred as an indicator of treatment adequacy in drinking water supply systems (MOH, 1982).

Test Method. Total coliforms are analyzed by the Water Quality Laboratory using the membrane filter test and are reported as colony forming units (CFU) per 100 millilitres (mL). The total coliform bacteria test measures the quantity of bacteria capable of producing a red colony with a green sheen on an Endo-type growth medium containing lactose within 24 hours at 35°C. The total coliform bacteria test is used by the Department to indicate the presence of sewage and/or storm water contamination and ensure compliance with the regulations.

Regulatory Limits. In disinfected drinking water, the Canadian and BC maximum acceptable concentration is zero total coliforms per 100 mL in all samples. Since total coliform bacteria are not uniformly distributed in water and are subject to considerable variation, the maximum acceptable concentration is interpreted as

  • No sample should contain more than 10 total coliform organisms per lOO mL.
  • No consecutive sample from the same site should show the presence of coliform organisms
  • Not more than 10% of the samples based on a minimum of 10 samples should show the presence of coliform organisms.

3.1.2. BACKGROUND BACTERIA

Background bacteria are used as a general measure of the bacterial population present in a drinking water system or in the raw source water. Under increasing nutrient conditions and/or a reduction in the concentration of chlorine residual, the background bacteria may increase and provide an early warning of the potential growth of coliforms.

Test Method. Background bacteria are analyzed by the Water Quality Laboratory using membrane filtration and reported as colony forming units (CFU) per 100 mL. The background bacteria test measures the quantity of bacteria capable of growing on an Endo-type growth medium containing lactose within 24 hours at 35°C.

Regulatory Limits. In disinfected drinking water, the Canadian maximum acceptable concentration of background bacteria is 200 colonies per 100 mL. In 2000, there was no BC regulatory limit for this parameter.

3.1.3. FECAL COLIFORMS

Fecal coliform bacteria are a subset of the total coliform bacterial group and are also are found in human and animal intestinal wastes. However, they are a more precise indicator of the presence of sewage contamination than total coliforms. The fecal coliform bacteria group includes the genera Escherichia and, to a lesser extent, Klebsiella and Enterobacter.

Test Method. Fecal coliforms are analyzed by the Water Quality Laboratory using the membrane filter method and are reported as colony forming units (CFU) per 100 mL. The fecal coliform bacteria test measures the quantity of bacteria capable of producing gas from EC medium within 24 hours when incubated at 44.5°C.

Regulatory Limits. In disinfected drinking water, the Canadian and BC maximum acceptable concentration of fecal coliforms is zero fecal coliforms per 100 mL.

3.1.4. HETEROTROPHIC PLATE COUNT BACTERIA

Heterotrophic plate count bacteria (HPC2D) are used as a general measure of the bacterial population present in a drinking water system or in the raw source water. Under increasing nutrient conditions and/or a reduction in the concentration of chlorine residual, the heterotrophic bacteria are usually the first group to increase and provide an early warning of the potential growth of coliforms.

Test Method. HPC2D is analyzed by the Water Quality Laboratory using membrane filtration. HPC2D counts are reported as colony forming units (CFU) per 1.0 mL. The HPC2D test measures the quantity of heterotrophic bacteria capable of growing on R2A Medium within 48 hours at 35°C. The HPC2D test is used to monitor the disinfection of the water at the disinfection plants, to track the decline in chlorine residuals in the distribution system and in the balancing reservoirs and to ensure compliance with the regulations.

Regulatory Limits. In disinfected drinking water, the Canadian maximum acceptable concentration of HPC2D is 500 colonies per mL. In 2000, there was no BC regulatory limit for this parameter.