Testing Water for Open Water Swimming

Water Quality & Testing Guidance

In recent years, open water swimming has increased in popularity significantly within the UK. With this occurring, swimming enthusiasts have been leaving the nice warm (and chlorinated) pools and relocating their sessions to recreational open water locations.

Therefore, training facilities and safe swimming sites are in high demand. As a result, there are an increasing number organisers and venue operators that are unsure as to whether their water body needs testing, and if so, for what.

Although performing water quality testing isn’t explicitly mandated in the United Kingdom, every operator must abide by a “duty of care” under the UK Common Law. If permitting swimming to take place, it’s required that the event organiser or venue owner should take reasonable care to guarantee optimal health and safety for everybody involved. Therefore, water quality testing should be a consideration in addition to the other safety measures such as signage and lifeguards.

There’s an increased risk of infection or illness when swimming in open water than in a treated pool. Because of this, having a fundamental understanding of the water quality of your water body can lower the chances of swimmers falling ill, ensure operators are meeting their duty of care requirement, whilst also following industry best practices.

Why should open water be tested?

The primary purpose of getting open water tested for swimming comes down to the existence of harmful microorganisms in the water. A collection of these microbes can cause severe health effects, resulting in swimmers falling ill. The main things to be looking out for, when testing open water for swimming activities are:

  • Bacteria – specifically measured through levels of E.Coli & Enterococci, which are typically found in faecal matter (human & animal) and indicate the presence of harmful pathogens in the water body. These are not visible to the human eye, and so the only effective way to detect them is through labatory analysis.
  • Blue-green algae – also known as Cyanobacteria, has over 50 different species that could cause health defects. Blue-green algae blooms when excessive amounts of algae start to grow quickly. Usually, this becomes apparent within slow-moving, warm waters and can be most problematic during the warmer summer months. Whilst algae is visible, the only accurate way to know the true levels of algae present is through microscopic analysis.
  • pH levels – needs to be tested to match the levels of the human skin. Safe pH levels are anywhere between 6 to 9. Guaranteeing this radically reduces the occurrence of potential health issues, particularly around skin and eye irritation, and it’s also mandated for British Triathlon sanctioned events.

What does water quality testing sample for?

As seen above, the overall quality of water isn’t influenced by a single element. Instead, several different factors determine if the water is safe for open water swimming. To determine the water body’s overall quality, samples are analysed for the following:

  • E.Coli
  • Faecal Streptococci / Intestinal Enterococci
  • Ph levels
  • Blue-green algae

Testing is designed to give an accurate indication of the water quality to help organisers, operators and swimmers alike to make an informed decision as to whether it’s safe to swim.  Results should be aligned to the EU Bathing Water Standards (for microbiology) and the Worlds Health Organisation guidance limits for Blue-green algae, and accredited labs and testing services should be able to provide an interpretation of these, against these thresholds.


Water quality testing isn’t exact science because any harmful pathogens can quickly occur based on the climate, weather, environment, atmospheric pressure, and various other elements.

Consequently, having a robust and regular testing program in place is the best method of demonstrating optimal “duty of care”. Although water quality testing isn’t compulsory, following this practice will undoubtedly protect both swimmers and operators as best as possible.

After reading the above, you should have a broader understanding of water quality testing. Feel free to contact us for further information or check out our in-depth results guidance page.


Blue Green Algae Testing

Click to find out more about our blue green algae (cyanobacteria) testing service.

We provide water quality testing services for:

Open water swimming venues


Triathlon events




TV & film productions


Fire services & local authorities


Private land owners

Arrange your water quality testing now or contact us on 01279 912950