Types of microbiological testing
Water samples are tested to make sure the drinking water is free from illness-causing bacteria. These tests look at the number of bacteria which are present, and liable to grow. This is the Total Viable Count, or TVC. The water is tested at both 22°C and 37 °C. The lower temperature shows the levels of bacteria which can grow at average room temperature. The higher temperature is equivalent to human body heat and will detect bacteria such as coliforms which can grow at body temperature. If E. coli is found in a drinking water sample, or other similar bacteria, this indicates faecal contamination in the water, and that it’s not safe for drinking.
Many companies carry out one set of water tests at a temperature of 30°C to detect both pathogenic and environmental bacteria. This general measure of water quality will also provide a TVC number. A low result means a low level of bacteria in the water. Higher results in the region of 10,000 colony forming units (CFUs) per millilitre of water is a sign that there may be an issue with biofilm contamination.
The Health and Safety Executive in the ACOP L8 and HSG274 documents set out clear protocols for the testing and detection of Legionella in water systems. Under certain circumstances, for example if a business has cooling towers or spa pools, there’s a legal requirement to take water samples from these to test for the presence of Legionella bacteria.
What Bacteria can be present?
Bacteria are microscopic organisms that can survive in many different environments. Several species of Bacteria are pathogenic, meaning they can cause infection, disease, or illness in other living things. They can also be parasitic, meaning they live off other living things, but can cause illness in the process.
They usually enter the water supply when the source water becomes contaminated. Some of the bacteria which can be found include:
One of the most dangerous bacteria that can form ion your water supply. Legionella bacteria can grow at an unprecedented rate in the correct conditions and can cause a serious, potentially fatal illness known as Legionnaires’ disease. Contaminated building water systems are responsible for most Legionnaires’ outbreaks.
This is a coliform bacteria, however it does not live for very long in water BUT it can be an indication of recent contamination. The E. coli species found in water are generally harmless bacteria but are used as an indication of the possibility of other similar bacteria being present which may cause problems.
These are a group of environmental bacteria that have originated from the intestines of animals. They tend to grow in the environment and are known as indicator organisms, i.e. they are used as a guideline of possible contamination. In the majority of cases where coliforms are picked up in water samples taken from a tap, the cause is that the tap needs cleaning.