UNDERSTANDING THE IMPORTANCE OF TOTAL VIABLE COUNTS (TVC) IN SAMPLING AND ANALYSIS

Total Viable Counts (TVCs) is not a specific micro-organism but rather a test which estimates total numbers of viable individual micro-organisms present in a set volume of sample.

Colony counts is important as it enables us in assessing the efficiency of water treatment and the integrity of the water system.

All cells are counted, including bacteria, yeasts and moulds. For instance, when determining total microbial count in water, a known volume of water is mixed with molten yeast-malt extract agar and given time to solidify.

One set of plates are incubated at 37°C for about 24 hours and the other set of plates are incubated at 20-22°C for 3 days.

Typically the TVC test is undertaken at 22°C and 37°C for drinking water and most other types of water, and at 30°C for cooling tower samples. It helps to evaluate the efficiency of certain water treatment processes like coagulation, flocculation and disinfection. It also gives an indication of the level of cleanliness of the water distribution system.

Colony counts are enable a count to be determined of the general population of heterotrophic bacterial present in the water. The bacteria grown in these tests are not indicators of faecal contamination, although historically the count at 37°C was taken to give an indication of faecal contamination. However, Total Viable Counts (TVCs) monitoring can be useful to determine the water quality and detecting potential sudden deterioration in water quality. An increase in the colony counts at 37 °C can be a sensitive indicator of ingress and further investigations need to be undertaken to establish the source.

Coliform bacteria are found in soil, vegetation and surface waters, and the intestines of warm-blooded animals and humans. Coliform bacteria in drinking water indicate that other disease-causing organisms (pathogens) may be present.

Escherichia coli (E. coli) is found in the intestines of humans and animals and, while some types live in the intestine quite harmlessly, others may cause diseases.

The Rationale for Sampling

The rationale for any sampling programme is to test if the control scheme in place is effective or not.

The Correct Procedures for Taking Samples

It is recommended that samples be only collected by people who are suitably trained to carry out the job in a safe and competent manner.

Sampling is a relatively simple task, but it is important the correct procedures are followed or the results can quickly become meaningless, for instance if the dirty hand of an engineer contaminates the sample bottle.

At SMS Environmental, we make every effort to ensure all samples are taken by suitably trained, disciplined personnel, taking the appropriate precautions with regards to personal hygiene and safety. In order to ensure all our samples are collected and transported using the highest standards, we stick to a strict protocol set out in our own method statements and in line with British Standards and UKAS ISO 107025 requirements.

Sterile sample bottles are used and care is taken to avoid accidental contamination of the sample during collection and subsequent handling.

Incubation Time for and in the Laboratory

UKAS accredited for potable & process water.

The incubation time is 18 hours. A further 2-3 days may be required depending on the test if the sample is positive.

The results are expressed in cfu/ml or cfu/0.1ml.

Useful Guidance

The UK water supply is governed by an EU directive on water supply and water quality. This directive has been introduced in the UK as the Water Supply (Water Quality) Regulations 2000, and is regulated by the Drinking Water Inspectorate.

For more information on our TVC Sampling and Analysis services please call 0800 138 21 21 or use the form below