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Water sampling in the process of collecting water from your supply for microbiological testing to ensure it remains safe for human consumption.
Water sampling is the process by which water is collected from a system for further microbiological testing. For both the sampling and testing processes there are very clear British Standards laid out to ensure accurate results.
Routine water sampling helps to determine the actual quality of your water supply and ensure that all parts of your system are working as they should so that the water coming through your pipes remains fit for purpose.
To paint an accurate picture of your water’s hygiene we recommend keeping a record of the TVC (Total Viable Count) results from each water sampling session. While there is no acceptable value or range for TVC results, by looking at trends over time you can establish whether there has been an increase in the bacteria present which may require further investigation into the health of the water system.
For drinking water sampling, the most common tests carried out are for TVC, legionella and E. coli.
TVC tests look at the number of live bacteria in every ml of water and are usually run at an ‘ambient’ temperature (22oC) and a bodily temperature (37oC). The test run at the lower temperature looks at the level of mostly harmless environmental bacteria while the test run at body temperature identifies bacteria that is more likely to harm users if consumed. There is no strict guide for what the TVC level should be but an increase in these levels may indicate that your supply is contaminated.
E.coli and other coliform bacteria are known as indicator organisms as, if found, their presence indicates that other similar and more harmful bacteria could be present. When testing, no coliform bacteria should be found within the supply as by UK law this makes it unsafe for consumption.
Legionella is a form of bacteria that grows quickly in stagnant or slow moving water and can lead to conditions like Legionnaire’s disease. In ACOP L8, The Health and Safety Executive outlines the specific protocols required for the testing and identification of Legionella. If a potable water source is found to contain more than 100 colony forming units per litre then immediate action should be taken such as the cleaning and disinfection of nearby outlets.
At the start of any microbiological testing, all water sampling should be done in accordance with British Standard BS 7592 which outlines the best practices for any parts of the sampling process that could affect results like flushing time.
When taking these samples it is also vital that there is no cross contamination which could lead to incorrect results or false positives. To avoid contamination, those in charge of collecting the sample will need guidance or training.
We recommend taking the lid off the sampling bottles as late as possible and replacing it straight away once the sample is completed. Before use, the bottles should also be sterilised and include a chemical (usually sodium thiosulphate) to neutralise any residual chlorine found within the water. All samples should then be labelled with a unique number alongside details on when and where it was taken.
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