A Guide on How to Correctly Take a Legionella Water Sample

Legionella sampling is carried out to assess the presence of Legionella bacteria within a water system. Legionella bacteria can develop in man-made water systems such as domestic hot and cold-water systems, cooling towers, and spa pools, particularly where water temperatures and conditions allow bacterial growth. Inhaling small droplets of contaminated water can lead to Legionnaires’ disease, a potentially serious form of pneumonia.

Why Legionella Water Sampling Matters

Routine Legionella water sampling helps identify potential risks, supports compliance with health and safety guidance, and assists in ensuring that water systems are being managed safely and effectively.

Taking a Legionella water sample correctly is one of the most important steps in any water hygiene monitoring programme. Done correctly, sampling provides objective, evidenced data on whether Legionella bacteria are present within your water system and whether your control measures are working as intended. Done incorrectly, a sample can produce invalid or misleading results that give a false picture of risk.

Legionella bacteria can develop in a wide range of man-made water systems where conditions allow bacterial growth. If you are not yet familiar with the specific risks Legionella poses in your workplace, our guide to Legionella risks in your workplace is a useful starting point before reading on.

At Swiftclean, our water hygiene specialists carry out Legionella sampling as part of planned monitoring programmes across a wide range of sectors, including healthcare, education, hospitality, and commercial property. This guide sets out the correct procedure for taking a Legionella water sample, what happens once it reaches the laboratory, and what to do with the results.

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Watch Our Video About Legionella Water Sampling

Watch our short video covering everything you need to know about Legionella water sampling, including temperature parameters, the types of sampling Swiftclean offers, and what to expect once your samples have been collected and sent for analysis.

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If you do not yet have a Legionella risk assessment in place to determine which outlets require sampling and at what frequency, read our step by step guide on how to conduct a Legionella risk assessment before setting up your sampling programme.

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Prefer to watch rather than read?

Our Technical Sales Consultant Dan walks you through the full water sampling process in the short video below.

Follow These Steps to Take a Valid Sample

Read below for our simple to follow, 9 step guide, to correctly taking a water sample.

Before you begin: what you will need

• Sterile sample bottles provided by your UKAS-accredited laboratory
• Sample submission sheet from the laboratory
• Labels for each sample bottle
• A calibrated thermometer for recording outlet temperatures
• A clean surface on which to place bottle caps
• Courier or drop-off arrangement confirmed in advance

Step 1

Ensure the outlet is clean and free from any attachments, including flow straighteners and aerators.

Step 2

Remove the sample bottle cap by breaking the seal and place the cap facing upwards on a clean worktop.

Step 3

Place the sample bottle beneath the outlet without touching the outlet itself. Turn on the cold tap to produce a steady flow of water and fill the sample bottle. Immediately replace the cap once the sample has been collected.

Some samples may require:

• A first draw sample (water taken immediately from the tap), or
• A flushed sample (allow the water to run for 2–5 minutes before sampling).

Step 4

Once the sample has been taken, record the temperature from the sample outlet on the sample submission sheet.

Step 5

Label the sample bottle with:

• Time
• Date
• Sample location
• Water source
• Sample reference number

Any attachments removed from the outlet should then be refitted.

Step 6

Once all samples have been collected, they should be delivered to a designated drop-off location, where they will be collected by courier for transport to the laboratory. For a Legionella sample to remain valid, it must reach the laboratory within 24 hours of collection.

Step 7

Upon receipt, the laboratory will:

• Log the sample
• Check the sample condition and temperature
• Analyse the sample for the requested parameters
• Compare the results against UK drinking water standards

The incubation period for a Legionella culture is 14 days. However, the laboratory will normally notify us if there are signs of Legionella growth after approximately 5 days and again at 10 days.

If no growth is detected, the results are generally received after the full 14-day incubation period has been completed.

Timeframe	What Happens
On receipt	Sample is logged, condition and temperature checked, and analysis begins
Day 5 (approx.)	Laboratory notifies if signs of Legionella growth are detected
Day 10 (approx.)	Second notification issued if growth signs continue
Day 14	Full incubation period complete. Results issued if no earlier growth detected

Water quality and the presence of Legionella bacteria can be affected by factors you may not immediately associate with your water system. Our blog on making sure there isn’t something in the water covers some of the less obvious contributing factors worth being aware of as part of your wider water hygiene programme.

Step 8

The results are compiled into a report by our Service Delivery Team and uploaded to the customer portal, where they can be accessed by the client at any time.

Step 9

The sample results are reviewed with our Technical Sales Team, and any required remedial actions are arranged.

Swiftclean holds Legionella Control Association accreditation, providing independent verification that our water hygiene processes meet the LCA code of conduct. Find out more about our renewed LCA certification and what it means for our clients.

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Your Legionella Water Sampling Questions Answered

Where can I get sample bottles from?

You can obtain sterile water sample bottles for Legionella testing from several sources in the UK:

• UKAS-accredited laboratories – Most laboratories that carry out Legionella analysis will provide the correct sterile sample bottles, labels, and submission forms when booking testing.
• Water hygiene and Legionella specialists – Many water treatment companies supply sampling kits as part of their services.
• Environmental testing suppliers – Specialist laboratory consumable suppliers sell sterile sample bottles suitable for microbiological testing.
• Local authorities or water companies – In some cases, particularly for private water supplies, councils or water providers may provide sampling bottles.

It is important to use the correct sterile sample bottles provided by the testing laboratory, as they may contain preservatives required for accurate microbiological analysis. The bottles should not be rinsed before use.

Where can I find UK drinking water standards?

UK drinking water standards are set out in the Water Supply (Water Quality) Regulations 2016, which establish the legal quality standards that water suppliers must meet when supplying water for drinking, washing, cooking, and food preparation. The regulations are enforced by the Drinking Water Inspectorate in England and Wales, with equivalent regulations applying in Scotland and Northern Ireland.

For Legionella sampling purposes, results are compared against these standards as well as against the specific guidance set out in ACOP L8 and HSG274, which provide the framework for managing Legionella risk in man-made water systems. A UKAS-accredited laboratory will compare your sample results against the relevant parameters and flag any results that fall outside acceptable limits.

You can access the full regulations at The Water Supply (Water Quality) Regulations 2016 on legislation.gov.uk. If you are unsure how to interpret your sample results in the context of these standards, our water hygiene specialists are happy to help.

What do I do when I receive my sample results?

Once you receive your Legionella sample results, the next steps will depend on whether the results are satisfactory or indicate elevated bacterial levels.

It’s advisable to discuss the results with a water hygiene specialist such as Swiftclean who can help interpret the findings, assess the level of risk and recommend appropriate corrective actions.

What is the next step if Legionella bacteria is confirmed on my site?

If Legionella bacteria is confirmed on your site, it is important to act promptly to reduce the risk of exposure and bring the water system back under control. These are the steps to take:

• Review the laboratory results
• Inform the Responsible Person
• Carry out a risk assessment review
• Implement immediate control measures
• Arrange remedial works or disinfection
• Retest the system
• Document all actions taken
• Continue ongoing monitoring

Aaron, our Technical Sales Consultant explains this in further detail in the video below

How often should Legionella water sampling be carried out?

Sampling frequency is determined by your Legionella risk assessment and written scheme of control rather than a single universal requirement. Some systems require monthly sampling, others quarterly or annually, depending on the level of risk identified.

ACOP L8 and HSG274 provide guidance on appropriate monitoring frequencies for different system types. If you are unsure how often your system should be sampled, a review of your risk assessment by a qualified water hygiene specialist is the right starting point.