Received a Positive Result?

If you have already received a confirmed positive Legionella result, this guide covers routine sample collection. For guidance on next steps, disinfection, and post-flush resampling, jump to the Results & Limitations page or visit our Resampling section below.

Step 1: Place Your Order

The number of samples depends on what you’re testing and how your water system is set up.

Not sure how many samples you need? Use our sample calculator to determine the right number for your property.

A minimum of 2 samples is typically taken from Representative Hot + Cold Samples.
— we’ll flag if more coverage is recommended once we see the details.

Buy Testing Kits

Step 2. Take Your Samples

Person washing hands under a running faucet in a Washroom setting

Before collecting your sample:

  • Wash and dry your hands thoroughly then sanitise your hands with hand sanitiser.
  • Do not open the bottle until you are ready to take the sample
  • Do not touch the inside of the sample bottle or lid
  • Do not rinse the bottle before use
  • Do not add anything to the bottle

All sample bottles are sterile. Any contact with hands, surfaces, or other materials can introduce bacteria and affect results.

Bathroom sink with running water and a mirror reflecting the room.

Prepare the tap or outlet

  • Remove any hoses, spray attachments, or filters
  • If the outlet is visibly dirty, wipe the outside only using a clean cloth
  • Do not disinfect, flame, or chemically clean the outlet unless specifically instructed

The purpose of sampling is to test the water supplied at the outlet, not to introduce cleaning agents that could affect results.

Person pouring water from a container into a sink with a faucet.

Collect the water sample

To take the sample:

  • Remove the lid and Place the bottle under the tap, turn on the tap slowly to avoid splashing
  • Adjust to a steady, moderate flow
  • Carefully open the sample bottle, holding the lid on the outside only
  • Fill the bottle to the marked line or as instructed
  • Do not allow the bottle or lid to touch the tap, sink, or your hands

Once filled, replace the lid immediately and tighten securely.

Aqua Samples sterile water sample bottles

After the sample is taken

After sampling:

  • DO NOT REOPEN THE BOTTLE AS THEY HAVE A LOCKING PROCESS.
  • Check the bottle is fully sealed, (turn upside down and give a gentle squeeze) if not tighten lid a little more and repeat.
  • Apply labels provided, ensuring details are clear and legible
  1. Sample Type
  2. Location
  3. Date/Time

Avoid placing the sample near heat sources or in direct sunlight.

White delivery box with 'aqua samples' and 'Next Day Delivery' text on a light gray background

Storage and return of samples

To return your sample correctly:

  • Store the bottle in a cool place until posting
  • Samples must be returned to the lab on same day as taken.
  • Use the box provided and pre paid envelope for sending to lab. 
  • Obtain proof of postage when sending the sample back

Delays in returning samples may affect the condition of the water at the time of analysis.

Common water sample contamination mistakes with labeled images and explanations.

Common causes of sample contamination

The most common reasons for contaminated water samples include:

  • Touching the inside of the bottle or lid
  • Placing the bottle down with the lid removed
  • Coughing, sneezing, or breathing directly into the bottle
  • Sampling immediately after cleaning or disinfecting the outlet

Avoiding these actions helps reduce the risk of external contamination.

Step 3. Drop Off Your Sample

Royal Mail Aqua Samples

Drop off Samples

Step 3. Drop Off Your Sample

Seal the box and hand it in at any Royal Mail Post Office counter — with 11,000+ locations across the UK, there's always one nearby.

Critical Requirements:

  • Post by 2pm for same-day Royal Mail collection
  • Return within 24 hours of sample collection
  • Use Royal Mail only with the prepaid packaging provided
  • Keep your receipt as proof of postage

Important: Samples posted after 2pm may miss same-day collection and exceed the 24-hour window, voiding your results.

For full details on sample return requirements, timing, liability, and best practices, see our Sample Return Policy.

Results will arrive to your inbox in 10-14 days.

Step 4. Understanding Your Results and Next Steps

Your UKAS-accredited laboratory results will be emailed as a PDF certificate.

• Legionella or combined Legionella & TVC testing: Results are normally issued within 10 to 14 days of the laboratory receiving your samples.
• TVC-only testing: Results can normally be issued within 7 days of the laboratory receiving your samples.

The certificate includes:
- Sample identification and location details
- Test results for each sample
- Detection levels (if bacteria are present)
- Laboratory accreditation details
See an example certificate below to understand the format and information you'll receive.
Download Example Certificate (PDF)

Understanding Your Results and Next Steps

Legionella Results (200ml Sample Volume)

Suspect (presumptive)

A Suspect (presumptive) of Legionella has been detected.

Result:
Awaiting confirmation

What this means:
Precautionary measures


Recommended action: following precautionary measures until the final confirmed result is received:

  • Clean and disinfect the affected outlet.
  • Flush the outlet twice daily for five minutes, taking care not to create aerosols.


Check the water system for any redundant pipework or "dead legs". These are sections of pipe where water can become stagnant due to little or no flow. Stagnant water encourages biofilm formation and can provide conditions that support the growth of Legionella and other waterborne bacteria. Any identified dead legs should be removed or modified to restore adequate water circulation.

Not detected

Legionella was not detected in the sample at the time of testing.

Result: Not detected (<20 cfu/L; corresponds to a rating of 4 on the certificate scale).
What this means: No evidence of Legionella growth at this outlet

Recommended action: Continue routine monitoring and normal water management. Keep results on record.

Moderate count

A moderate level of Legionella has been detected.

Result: 20–200 cfu per 200 ml (≈ 100–1,000 cfu/L)

What this means: System conditions may be supporting bacterial growth

Recommended action:

Clean and disinfect the affected outlet as soon as possible.

Continue flushing the affected outlet twice daily, taking care to minimise the generation of aerosols, until satisfactory results have been confirmed.

Where fitted, inspect and consider replacing any flexible hoses, as these can contribute to bacterial colonisation.

Investigate system controls, inspect tanks and pipework and carry out follow-up sampling using the post flush method.


Where fitted, inspect and consider replacing any flexible hoses, as these can contribute to bacterial colonisation.




High count

A high level of Legionella has been detected.

Result: Greater than 200 cfu per 200 ml (>1,000 cfu/L)

What this means: Elevated bacterial growth indicating increased risk

Recommended action: Immediate review of the system. Following recommendations below until system disinfections has been completed. Refer to your Legionella Risk Assessment /written scheme of works and seek specialist advice. Repeat sampling after works are complete.

Clean and disinfect the affected outlet as soon as possible.

Continue flushing the affected outlet twice daily, taking care to minimise the generation of aerosols, until satisfactory results have been confirmed.

Where fitted, inspect and consider replacing any flexible hoses, as these can contribute to bacterial colonisation.

Investigate system controls, inspect tanks and pipework and carry out follow-up sampling using the post flush method.

TVC (Total Viable Count)

Low

Low general bacterial activity.

Result: <100 cfu/ml

What this means: Typical of good water quality and regular turnover.
Within acceptable range


Recommended action: Continue routine monitoring.

Moderate

Moderate bacterial activity detected.

Result: 100–1000 cfu/ml

What this means: May indicate stagnation, reduced use, or temperature issues

Recommended action: Flush outlets, review usage and temperature control, and repeat sampling.

High

High bacterial activity (>1000 cfu/l)

Result: >1000 cfu/l

What this means: Indicates significant bacterial contamination and likely system colonisation.

Recommended action:
Tank/system clean recommended
Retest 72 hours after disinfection and continue frequent testing until satisfactory control is achieved.

Resampling After a Positive Result

If your results indicate resampling is required — whether for Legionella or an elevated TVC — please follow the guidance provided with your laboratory report and refer to our Results & Limitations page for recommended next steps.

For Legionella resampling specifically, the post-flush method must be used following disinfection of the affected outlet(s). This is distinct from routine first-draw sampling and is essential to confirm that remediation has been effective before the outlet is returned to use.

For TVC resampling, standard pre-flush (first-draw) sampling applies unless otherwise advised.

For full guidance on sampling methods and what to do following a positive result, visit our Results & Limitations page.

Order Resample

Final Notes

Your test report should be retained as part of your water safety records and reviewed alongside your risk assessment.

Important: Understanding Test Limitations

Water testing provides valuable information to support your water safety management programme. However, it's important to understand what results do and do not guarantee.

For full details on test limitations, sample requirements, liability, and what results cannot confirm, see our Results & Limitations page.

Need More Help?

We're here to support you throughout your water testing journey: