No.: 98-09E
August, 1998

Introduction

All water that is used for domestic purposes must be free from disease-producing organisms or "pathogens". Although water treatment techniques and disinfection have resulted in a dramatic decrease in the occurrence of water related illness, the occasional outbreak of waterborne diseases indicate the need to maintain surveillance programs on our drinking water supplies.

Monitoring for Disease - The Total Coliform Count

Many organisms which cause disease in humans originate from sewage or human excrement. Consequently, surveillance programs use bacteria commonly found in these contamination sources as a measuring device to establish the safety of drinking water. The most widely used test for this purpose involves estimating the number of coliform bacteria in a water sample.

Coliform bacteria are always present in fecal wastes and greatly outnumber disease-producing organisms. Given this, and the fact that most pathogens originate from sewage and feces, coliform levels are considered to provide a good indication of whether or not disease carrying organisms may be in the water. If there are coliform bacteria present in a water sample it indicates that pathogens could also be present. Alternatively, if coliform bacteria are absent in a water sample, it indicates that pathogens are probably also absent.

Lab results for coliform bacteria are measured in colony forming units (CFU’s) as they tend to grow in colonies. Manitoba utilizes the values set out in the current edition of "Guidelines for Canadian Drinking Water Quality", produced by Health Canada, as the criteria for establishing drinking water quality. Based on this criteria, the maximum acceptable concentration for coliforms in drinking water is zero organisms per 100 ml.

If lab results indicate the presence of coliform bacteria, the local Public Health Inspector (PHI) should be consulted. The PHI will prescribe the appropriate corrective actions to be taken. The most common immediate action is to re-sample to confirm that coliform bacteria are present. If resampling confirms that the water supply is contaminated additional actions will be required.

In the case of a private water supply, additional action may include disinfecting the water source (if it is a well), the water treatment equipment (e.g. filters etc), and the water storage equipment (e.g. cisterns). In the case of a public water supply, additional action may include increasing the chlorine dosage, disinfecting and cleaning the water treatment equipment and reservoirs, as well as flushing, disinfecting and swabbing the watermains. In extreme cases, an alternative water source may have to be sought or a boil advisory placed on the system.

Monitoring the Water System - The Heterotrophic Plate Count

The general bacteria population in a water sample include organisms such as iron bacteria, which are unrelated to sewage or fecal wastes. The heterotrophic plate count (HPC), formerly known as the standard plate count (SPC), is an analysis which provides a count of these organisms. Because the HPC includes non disease carrying bacteria, it does not indicate the presence or absence of disease carrying organisms. Rather, the HPC analysis is used to provide and indication of the general sanitary condition of the water.

HPC analysis is often used as a diagnostic tool. A significant increase in HPC levels at a particular sampling point indicates a deterioration in the water quality in that portion of the water system, and corrective action may be required. Further testing could isolate the problem to a particular component of the water treatment plant such as the filters or the reservoir. It could also be used to identify problem sections of the water distribution system. Once the problem areas are identified the appropriate corrective action can be taken.

HPC analysis is also used to establish the accuracy of coliform results, as coliform counts are generally not considered reliable on water samples which have an HPC >(greater than) 500 CFU per ml. This occurs because the vast number of bacteria in a water sample of this nature interfere with the analytical method used to test for coliform bacteria.

Similar to coliform counts, HPC’s are measured in colony forming units. An HPC level of 500 per ml should be considered as an objective for drinking water although this is not a "set" water quality guideline.

Sudden increases in the HPC level should be considered as an early warning sign of possible problems in the water system. In private water systems, corrective action may include disinfecting the water source (if it is a well), the water treatment equipment, and the home plumbing system, including storage reservoirs.

In a public water supply, corrective action may include: disinfecting the water source (if the source is a well); increasing the chlorine dosage; examining components of the water treatment process; and watermain flushing, swabbing and/or disinfection.

The local Public Health Inspector should be consulted to provide guidance regarding the required corrective action and how it should be conducted. Inspectors may be contacted through the Manitoba Environment office nearest you as listed in the telephone directory under Government of Manitoba. The department has regional offices in Winnipeg, Brandon, The Pas, Selkirk and Steinbach.