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Swimming Pool Water Testing

Swimming pool water needs regular testing and treatment to ensure it is safe to use. The basic purpose of all pool treatment is to stop the spread of infection caused by harmful bacteria. The most common disinfectant used is chlorine. However, there are a complex range of factors that are essential for chlorine to be effective. Simple testing kits don’t cover all the necessary factors and are not always very accurate. Somerset Scientific Services provide UKAS accredited chemical and microbiological testing for public, private and commercial pools. Our packages offer regular professional checks to back up simple daily monitoring. Here’s our guide to what’s included in our testing package, and why it’s so important to monitor your pool.

Chemical Testing For Swimming Pools

We carry out basic chemical checks at the poolside each time we visit. These can include: free chlorine, combined chlorine, total chlorine, pH, cyanuric acid, alkalinity & calcium hardness.

  • Free chlorine is the disinfectant available in the pool to tackle bugs. Once it has ‘attacked’ a bug, it becomes combined chlorine (this is the strong, stinging chlorine smell you get in some pools) and total chlorine is the addition of the two.
  • Cyanuric acid is used in outdoor pools. Sunlight breaks down free chlorine rapidly, meaning it won’t be available to disinfect the pool. Cyanuric acid is added to stop this happening. However, too much cyanuric acid can be detrimental to the chlorine and inhibit it – it’s a very fine line, and something most pool owners may need professional help with.
  • Testing the pH level is essential for ensuring the correct balance between alkaline and acid is maintained.
  • Calcium hardness can cause white scum on metal elements of the pool. This is only an aesthetic issue but is something pool owners usually want to avoid.

In the lab, we can carry out almost every water analysis under the sun! This gives pool owners a gateway to an experienced laboratory should they get into some serious chemical issues with their pool. So many parameters could go wrong in a pool environment and sometimes it’s difficult getting labs to take interest in a new or small pool, which can be frustrating. By having us test their pool regularly our customers have access to this expertise should they need it.


Our normal suite of analysis includes E.coli, coliforms, TVC’s @ 22, TVC’s @ 37 & Pseudomonas. Units of these bugs are measured as cfu/100ml (colony forming units). This is a blanket suite of analysis which covers all basic bacteriological issues that might be expected in a pool environment. Bacteria thrive in a swimming pool environment – wet and warm – and are not visible to the eye, so testing really is essential. We can also test for other specific bacteria, such as cryptosporidium, if there are concerns they may be present.

  • E.coli is bought into the pool by faecal matter on bathers, and unfortunately it is more common than one would like!The failure limit <1, so if even one E.coli is present, it’s a failure. This is the same for all coliform bacteria. Many coliform aren’t a health risk themselves but can indicate a maintenance issue. E. coli can cause cramps, diarrhoea, vomiting and, in extreme cases, death.
  • Pseudomonas can cause skin rashes by infecting the hair follicles.
  • TVC stands for ‘total viable counts’. This isn’t a specific type of bacteria, it’s a general value of all organisms in the pool. They are grown at 2 different temperatures, 22 degrees & 37 degrees Celsius. Those grown at 22 are cold water bugs which may be present naturally in the water. Those grown at 37 degrees (body temperature) are a bit more concerning as they can harbour in the body.

Why use a professional water testing laboratory

Pool owners should already be checking chlorine and pH on a regular basis, and a slightly more advanced monitoring schedule should include cyanuric acid too. Our chemical tests are a reliable check that the client’s kit is working. The amount of chemicals can be mind boggling and someone without a scientific background might be overwhelmed. We advise on what chemicals are needed and are always on the end of a phone to assist if a problem arises.

Microbiological testing is something the client cannot do themselves. There are no obvious signs of bugs in the pool until someone gets ill. We suggest a monthly check for the normal range of microbes, and this hopefully will catch a contamination before it becomes severe. If we do find bugs, we contact the clients immediately and advise a solution to whatever contamination they have.

What are the risks in not getting your pool tested?

How do you know that your chemical kits are working? Are they accurate? Are you adding enough or too much chlorine? Is your pH level correct? Contamination can occur so easily, even from something as simple as a slight lapse in chlorine one day which allows the bugs to take over or a contaminated person entering the pool. If a microbiological contamination goes unnoticed, the bacteria can multiply at eye-watering rates and expose all users to serious infection. If you have a swimming pool that is used by public, at a hotel, holiday cottage, spa or sports centre, you have a responsibility to ensure your visitors’ health and wellbeing. You could even be liable to prosecution in the case of illness if you haven’t taken reasonable steps to maintain your pool.

Trusted & impartial advice from Somerset Scientific Services

We work to HSE (Health and Safety Executive) guidelines, as there is, surprisingly, no legislation currently set for swimming pool contaminants and chemistry. We are UKAS accredited for our microbiology analysis, excluding pseudomonas. Our staff have years of hands-on knowledge testing hundreds of different pools. We have practical experience in solving complex scenarios to share with our clients. Most importantly, we offer unlimited, impartial advice. We don’t sell any pool care products or chemicals, so you can be sure our assessment and guidance is in the best interests of you, your pool and its users.

Contact us to get a quote for your pool now.