What is Total Viable Count or TVC and What it Means for Water Quality?

In this article we take a look at water quality testing, focussing on total viable count or TVC, what this means, what it tells us about a water system and why you need to know about it if you’re involved with water quality monitoring.

Does your water contain bacteria?

All water supplies contain some bacteria. The question is, how much bacteria is in there… and how much of it is potentially harmful?

In the UK, water companies must make sure the water they supply to homes and businesses is safe to use. The assumption is that the supplies must be fit to drink, this is called potable water. Typical water supplies will contain bacteria, as noted above – the average glass of tap water will have millions of bacteria present. Most of it is perfectly safe, however.

Why test your water for total viable count?

Water companies use a range of methods to make sure harmful bacteria is removed from their water during the treatment process. These methods mean that once it is piped to homes and business, the water is safe to use. However, it is almost impossible to remove all instances of harmful bacteria from the water they supply.

So, what happens to the harmful bacteria when it enters a home or business premises?

Here, we’ll look at why water testing is important, and why anyone responsible for water safety should know about total viable count or TVC.

What does total viable count mean?

Many businesses will need to perform regular water testing. This is done to confirm the water is safe, that it does not have excessive amounts of harmful bacteria present, and that the treatment measures they have put in place are working as they should.

And this is where total viable count – TVC – comes in.

Total viable count or TVC refers to the total number of microorganisms that are present in a sample of water taken from a location within a water system.

There are specific processes involved in taking water samples, and that is a topic for another article. The test must be conducted in a certain manner to ensure the results are as accurate as possible. It should also be done by someone with relevant knowledge, training, and experience in doing so. In many instances, companies hire an external testing company to come in and handle this part of the water safety treatment and testing programme.

The total viable count can only be an estimate, but it does give a good idea of what is present in the water sample, and at what levels. It refers to how many live cells are present, along with those that are deemed viable. These can develop into colonies to take over the water system should they be given an opportunity to do so.

It’s important to remember that total viable count is not the same as the total bacterial count. This is commonly referred to as TBC, so it can be easy to confuse the two. However, the latter test confirms how many bacteria are present – including dead bacteria as well. Typically, then, this count is usually higher than the total viable count.

Water testing procedures will differ according to where they’re from

Regulations set out to monitor and maintain water quality, and safety will provide guidance on the processes used to test various samples. For example, the time taken to incubate a sample would differ depending on whether it is a sample of tap water or a sample taken from somewhere else, such as an evaporative cooling tower. Different temperatures would also be used in each case to ensure the most accurate results.

Is total viable count useful for legionella testing?

No, the TVC count gives us just that – the total number of bacteria present that could grow and develop within the part of the water system the sample was taken from. The total number will cover all types of bacteria found rather than testing for anything specific, such as legionella.

If it is necessary to check for levels of Legionella bacteria within a water system, a specific test for that bacteria alone must be conducted. A TVC test might also be done, but separate samples would be taken for legionella testing as well. The same applies with any other testing that is intended to check for something specific. A specific medium must be used in each case, hence why several samples may be required depending on the situation.

Is a high total viable count concerning?

High TVC results are of concern because it suggests there are more microbes and microorganisms in the water than there should be, indicating that the water may be “dirty” or the treatment programme is not working as it should.

Microbes feed on debris in water pipes, tanks, and other equipment, allowing them to multiply. They may eventually colonise the system, and this is difficult to remedy – hence why regular water testing is an essential component of a water safety programme. Prevention is far better than trying to deal with an issue if it arises, and determining the TVC of the water is a vital tool to help in doing this.

What does a high TVC count mean?

It may mean the water system is not being adequately cleaned and maintained. For example, a hot water tank might be cleaned, but not regularly enough and not thoroughly enough to prevent an overgrowth of bacteria.

It may also mean the water treatments added to the supply are not doing their job correctly. The chemical dosage rates may be too low, for example. The TVC test is a good starting point to identify whether any such issues could be present.

Prevention is better than cure when it comes to water quality

The total viable count testing is a good way of keeping an eye on the quality of the water and whether it is suitable for use. The TVC results will vary from one test to the next, but it should not vary by huge amounts. If a sharp rise is noted between one test and the next, further research should be conducted to identify the reason for the rise.

One method of doing this would be to take further samples that could be tested for individual organisms such as Legionella bacteria, Pseudomonas aeruginosa and E. coli among others. This will help narrow the possibilities and reveal the culprit. A high TVC also means changes will likely need to be made to the water treatment and maintenance plan. If these steps are put in place, it should help reduce the TVC back to acceptable levels.

Water testing and analysis should be conducted by experts who are aware of the processes involved. External companies such as Water Treatment Services often prove to be the ideal choice in such scenarios.

Water quality testing and expert analysis

Water Treatment Services offer a comprehensive range of water quality testing and analysis solutions for drinking water, surface water, groundwater and industrial effluent. Our experts can provide advice and support to help you determine water quality issues.

With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained technicians, in-field specialists and consultants we can offer professional, cost effective laboratory analysis solutions across the whole of the UK and internationally.

Contact us today to learn how our water quality analysis solutions can help you.