What should businesses consider when choosing a water testing laboratory?

The right water testing laboratory is one that can produce technically dependable results for the types of water systems being assessed and provide evidence that those results can be used in a business’s water safety arrangements. Selection should therefore go beyond price and consider the laboratory’s test scope, quality controls, independence, data management and ability to fit into the organisation’s wider compliance process.

1. Match the laboratory’s scope to the water system

Different premises and systems may require different types of analysis. A laboratory suitable for routine potable water samples may not be the best choice for samples from cooling systems, spa pools, industrial processes or complex hot and cold water installations. Before appointing a provider, confirm that it routinely handles the relevant sample types and can test for the organisms or indicators required by the site’s risk assessment.

This is particularly important where a business operates several types of system. Using one laboratory may be convenient, but only if its scope covers the full range of relevant samples. Otherwise, results may be split between providers, making trends and recurring issues harder to review.

2. Assess how results support risk-based decisions

Laboratory testing is one part of legionella control rather than a substitute for a competent risk assessment. A suitable laboratory should understand that a result needs to be considered alongside system design, water temperatures, usage patterns, maintenance records, control measures and any vulnerable people who may be exposed.

Businesses should establish how the laboratory presents results that may require investigation. It should be clear whether the service provides analytical results only or whether it can explain the significance of findings within the agreed scope of work. The laboratory should not be expected to make decisions that belong to the responsible person or appointed water safety professional, but its information should be sufficiently clear to support those decisions.

3. Examine quality assurance arrangements

Ask how the laboratory checks the reliability of its work. Relevant controls may include the use of documented procedures, equipment maintenance, calibration, internal quality checks, staff competence assessments and participation in suitable external quality assessment schemes. These arrangements help demonstrate that results are generated consistently rather than relying solely on an individual analyst.

It is also reasonable to ask how amended reports, questionable results and failed quality checks are managed. A reputable laboratory should have a documented process for investigating errors, recording corrective action and notifying affected clients where a reported result may need review.

4. Check independence and subcontracting arrangements

Businesses should understand who performs each stage of the service. If any analysis is subcontracted, the laboratory should explain which work is passed to another organisation, how that provider is selected and how the result is incorporated into the final report. This is relevant when several tests are ordered under one contract, as the apparent single point of contact may not be the organisation carrying out every analysis.

Independence also matters when results could lead to remedial expenditure or changes to a water management programme. The laboratory’s role, and any separate consultancy or remedial role, should be defined clearly so that responsibilities and potential conflicts are understood.

5. Consider sample traceability and records

Although the sampling process must be agreed separately, the laboratory should be able to maintain a clear audit trail from receipt of a sample to issue of the result. This normally includes a unique reference, receipt details, requested analyses, relevant condition checks and the identity of the work associated with the sample.

Good records make it easier to compare results over time, demonstrate what was tested during an audit and investigate an unexpected finding. Businesses should also confirm how long reports and supporting records are retained, who can access them and whether historic results can be retrieved in a usable format.

6. Review reporting and data arrangements in detail

A report should identify the premises or system, sample reference, date information, analysis undertaken, result and any relevant qualifications or limitations. Results should not be presented in a way that makes a negative finding appear to prove that a system is permanently free from legionella. Laboratory testing describes the sample examined at a particular point in time; it does not remove the need for ongoing control.

For organisations managing multiple sites, consider whether reports can be organised consistently and whether data can be reviewed by location, system, sample point and date. A clear results history can reveal repeated findings, missed sampling points or deterioration in control that may not be obvious from isolated reports.

7. Establish how urgent or unexpected findings are handled

Before commissioning testing, agree the process for communicating a result that is unexpected, potentially significant or affected by a technical qualification. The laboratory should identify the authorised contacts, the information it can provide and when further analysis or repeat sampling may be appropriate. This avoids uncertainty about who receives important information and what happens after a result is issued.

Businesses should also ask whether the laboratory distinguishes between a confirmed analytical finding, a result requiring verification and a sample that cannot be reported reliably because of a problem with its condition or identification. Those distinctions can affect the appropriate next step.

8. Compare the whole service, not just the test price

A lower quoted price may not represent better value if essential tests, administration, reporting or follow-up support are excluded. Obtain a clear schedule of what is included, including any separate charges for additional analyses, repeat work, site-specific reporting or data requests. The quotation should state the sample types, tests, reporting format and responsibilities of each party.

Also consider whether the laboratory can support the organisation’s likely requirements as its water management programme develops. Consistent processes, accessible records and a clearly defined service scope are often more useful than selecting a provider on the basis of a single isolated test.

Questions to ask before appointing a laboratory include:

• Does the laboratory’s scope cover every relevant water system and sample type?
• How are quality checks, equipment calibration and staff competence controlled?
• What happens if a result is technically qualified, unexpected or requires investigation?
• Is any work subcontracted, and how is that work controlled?
• What information will appear on the report, and how will results be stored?
• What is included in the quoted service, and which activities would incur additional charges?
• Can the laboratory provide consistent records that support audits and long-term trend review?

Businesses should record the reasons for their choice and review the laboratory periodically, particularly if the water systems, testing requirements or compliance arrangements change. The most suitable provider is the one whose competence, controls and service structure align with the organisation’s actual water safety responsibilities.