Results & Limitations
Our laboratory testing services are designed to help you monitor water quality and support your risk management and compliance processes.
It is important to understand the scope and limitations of sample-based testing.
Looking for help interpreting your test results? See our Water Sample Collection & Results Guide for detailed CFU/L breakdowns, action levels, and recommended next steps for Legionella and TVC results.
Sample Return Requirements
For accurate and valid results, all water samples must be returned to the laboratory within 24 hours of collection.
Samples not received within this timeframe may experience bacterial growth or degradation that will compromise result accuracy and void the test.
View full Sample Return Policy for detailed posting guidelines and requirements.
Snapshot in Time
Test results reflect the condition of the specific water sample at the time and location it was collected only.
Water quality can change due to:
- System use or stagnation
- Temperature changes
- Maintenance activities
- Flushing or cleaning
- Operational changes
For this reason, results should be considered a snapshot rather than a guarantee of ongoing conditions.
Not a Guarantee of Safety
A satisfactory or negative result does not guarantee that:
- Bacteria are absent elsewhere in the system
- Conditions will remain safe in the future
- Further control measures are unnecessary
Regular monitoring and good water management practices remain essential.
Not a Replacement for Risk Assessment
Our testing kits and reports do not replace:
- A Legionella risk assessment
- Professional technical advice
- Legal or regulatory responsibilities
Testing should form part of a wider water safety or control programme.
Duty holders remain responsible for managing risks within their premises.
Sample Limitations
Results depend on:
- Correct sample collection
- Proper labelling
- Suitable storage
- Timely return to the laboratory (within 24 hours)
Improper handling, delays, or contamination may affect accuracy.
We cannot accept responsibility for compromised samples caused by incorrect collection or transit conditions.
Pre-Flush vs. Post-Flush Sampling — What's the Difference?
The method used to collect a water sample significantly affects what the result tells you. There are two standard approaches:
Pre-Flush (First-Draw) Sampling
The sample is collected before the outlet is run or flushed. This captures the water that has been sitting stagnant in the pipework -typically overnight or longer. Pre-flush sampling is used for routine monitoring as it represents worst-case conditions at that outlet and is most likely to detect the presence of Legionella or elevated TVC if contamination exists.
Post-Flush Sampling
The sample is collected after the outlet has been flushed for a defined period - typically until temperatures are within specification (cold water below 20°C, hot water above 50°C). Post-flush sampling draws water directly from the incoming supply or distribution system rather than stagnant pipework. It is used specifically to verify that remediation has been effective following a positive result, disinfection, or system works.
Why It Matters
Using the wrong method can produce misleading results. A post-flush sample taken after routine flushing may return a satisfactory result even where contamination exists in stagnant sections of pipework. Always confirm with your water safety advisor which method is appropriate for your situation.
Positive Legionella Results & Post-Flush Resampling
If a confirmed positive Legionella result is returned, the affected outlet(s) must be taken out of use immediately, then cleaned and disinfected by a competent person. Following disinfection, resampling must be carried out using the post-flush method — samples are collected after the outlet has been flushed until temperatures are within specification, confirming that remediation has been effective.
This post-flush resample is distinct from a standard first-draw (pre-flush) sample and is essential to verify the system is safe before returning the outlet to use. We will notify you by email if a confirmed positive result is returned, with guidance on next steps and a link to order your resample kit.
If you are unsure how to proceed following a positive result, please contact us or seek advice from a qualified water hygiene specialist.
Interpretation of Results
Reports provide laboratory findings and general guidance notes only.
They do not constitute medical, legal, or engineering advice.
Customers are responsible for determining appropriate actions based on their specific circumstances.
If you are unsure how to interpret your results, we recommend seeking competent professional advice.
Liability
To the fullest extent permitted by law, we are not liable for decisions, actions, or losses arising from reliance solely on test results.
Our services are intended to inform decision-making, not replace professional judgement or statutory duties.
Questions
If you need help understanding your report or selecting further steps, please contact us — we're happy to guide you.