TVC Sampling

Total Viable Count (TVC) analyses are very useful for trend analysis whereby changes in the numbers of microbes present in a system can be monitored over time and multiple samples. This can reveal useful information regarding factors having an effect on TVC counts, e.g. If a count is substantially higher during summer months it is likely that the organisms in the system are flourishing in higher temperatures and a suitable control measure may include reducing the temperature of the system in the summer. 

A TVC test is only an estimate and results should be considered as an order of magnitude, e.g. less than 10, less than 100, less than 1000. A count of 50 cfu/ml obtained one month followed by a count of 60 cfu/ml would not be considered as significant based on the limitations of the procedure however a count of 50 one month followed by a count of 5000 the following month is clearly indicating a dramatic change to the system.

Drinking Water Inspectorate Recommendations

Our analytical service provider has provided us with the following guidelines for TVC samples issued by the Drinking Water Inspectorate (DWI).

Drinking Water Standard

Method: 2 days @ 37°C maximum 50 cfu/ml

Method: 3 days @ 22°C maximum 500 cfu/ml

Washroom Water Standard

Method: 2 days @ 37°C maximum 500 cfu/ml

Method: 3 days @ 22°C maximum 5000 cfu/ml