A Legionella risk assessment and a laboratory water test answer different questions. Knowing the difference helps landlords arrange the right service and understand the report they receive.
If you have been asked to arrange a “Legionella test” for a rental property, it is worth checking what is actually being requested. The phrase is often used when somebody means a risk assessment, but collecting a water sample for laboratory analysis is a separate process.
What does a Legionella risk assessment look at?
An assessment considers the hot and cold water system, how it is used and whether there are conditions that could allow Legionella bacteria to grow or create a risk of exposure.
Depending on the property and what is accessible, this can include:
- How hot water is produced and whether water is stored.
- Taps, showers and outlets that receive little use.
- Relevant water temperatures and the effectiveness of existing controls.
- Accessible tanks, cylinders and identifiable redundant pipework.
- Occupancy, periods of vacancy and relevant information about people using the system.
The system matters. Our guide to combi boilers, hot-water cylinders and water tanks explains why two similar-looking properties can need different considerations.
The result is an assessment of risk, with findings and appropriate recommendations. It is not a laboratory finding that bacteria are present or absent.
What does a water sample tell you?
Laboratory sampling involves collecting water using an appropriate method and having it analysed for Legionella. The result relates to the sample collected at a particular location and time.
That result needs to be interpreted alongside the water system and its risk assessment. A negative result should not be treated as a permanent guarantee that the whole system will remain free of Legionella, or as a replacement for managing the underlying risks.
Where sampling is appropriate, HSE guidance says samples should be tested by a UKAS-accredited laboratory participating in a suitable water microbiology proficiency testing scheme.
Does every rental property need laboratory sampling?
No. HSE advises that routine Legionella sampling is not usually required for domestic hot and cold water systems. The priority is to assess the risks and put suitable controls in place.
Sampling may be appropriate in particular circumstances. HSE gives examples including doubts about the effectiveness of the control regime, or recommended temperatures or disinfection concentrations not being consistently achieved. The decision should follow the circumstances of the system and competent advice.
This is why it helps to clarify whether an agent or landlord is asking for a risk assessment report or an actual laboratory result before booking.
Are temperature checks the same as testing for bacteria?
No. Taking water temperatures helps assess how the system is operating and whether temperature controls are effective. A thermometer does not detect Legionella bacteria.
Likewise, a water sample does not explain every feature of the system. For example, the way a property is used still matters: our article on Legionella risks in empty properties looks at how periods without normal water use can change the risk picture.
What should Scottish landlords have in place?
The Scottish Government’s Repairing Standard guidance says private landlords must ensure water systems are assessed for Legionella risk before a property is first let. It says the assessment should be reviewed at intervals of no more than two years, with a new assessment where a review identifies changed risk factors.
Depending on the system and their competence, landlords may be able to assess the risk themselves or appoint a competent assessor. A professional visit is an option for landlords who want help understanding the system and documenting the findings.
A report also needs to lead to appropriate action. Our guide to what to do after a Legionella risk assessment covers using the findings and keeping track of the next steps.
What does Thorn provide?
Thorn provides Legionella risk assessments for landlords and letting agents across Glasgow and East Dunbartonshire, carried out by an Elmhurst Energy Approved Legionella Risk Assessor.
The service considers the accessible water system, relevant observations and temperature readings, with a written report of the findings and recommendations. Routine laboratory water sampling is not included in this assessment service.
If you have been asked for a “Legionella test” and are unsure what is meant, Ask Wendy about the assessment service, what information is useful before a visit and guide pricing. If a laboratory result has specifically been requested, mention that when enquiring so the required scope can be clarified.
Guidance and further information
- HSE: Legionella and landlords’ responsibilities
- HSE: Testing and monitoring your water system for Legionella
- Scottish Government: Repairing Standard guidance, Annex D1, paragraphs D.28–D.35
Guidance checked on 2 November 2026.