What should you compare when selecting a water sample lab?

The most important comparison is whether the laboratory is suitable for the decisions your water management programme needs to make. Assess the laboratory’s technical capability, understanding of legionella control, sample acceptance process, result interpretation, data security, commercial terms and ability to provide consistent evidence for your compliance records—not simply its price.

Check that the laboratory can analyse the full range of samples your system may require. A building may need legionella analysis alongside other microbiological or chemical parameters, depending on its risk profile, system design and investigation requirements. Confirm that the laboratory can handle the relevant sample types and provide results in a form that can be compared over time. If several laboratories or subcontractors are involved, establish who is responsible for each part of the analysis and how the combined results will be controlled.

Assess its understanding of water system risk. Laboratory results are most useful when they are considered alongside the type of system, sampling location, temperature control, operational history and any remedial work. Ask whether the laboratory can explain the significance and limitations of a result without presenting it as a complete assessment of the system. A laboratory should not replace a competent risk assessor, but its technical team should understand how analytical findings support investigation and control decisions.

Compare how results are interpreted and escalated. Find out what happens when a result is unexpected, elevated or inconsistent with earlier samples. Useful questions include:

• Will unusual findings be checked before the result is issued?
• Can the laboratory identify when a repeat sample or further investigation may be appropriate?
• Will the laboratory distinguish between a confirmed result, a result requiring clarification and a result affected by a sample limitation?
• Does it explain terminology, units and reporting conventions clearly?

The laboratory should provide factual technical information while leaving site-specific control decisions to the responsible competent person.

Review the sample acceptance and rejection rules. A provider should state what information must accompany each sample, how containers must be identified, and the circumstances in which a sample may be rejected or qualified. Ask how it deals with missing site details, damaged containers, insufficient volume, illegible labels or samples that fall outside the laboratory’s acceptance criteria. Clear rules reduce the risk of receiving a result that cannot confidently be linked to the correct outlet, asset or sampling event.

Look at the information captured with each result. A useful laboratory record should allow the result to be traced to the relevant site and sampling point. Depending on the service, this may include the sample reference, location, collection date, receipt details, requested analysis and any relevant observations. Consistent identification is particularly important where a business manages multiple buildings or repeats sampling at the same outlets.

Examine the laboratory’s quality and governance arrangements beyond its formal accreditation status. Ask how it maintains staff competence, controls changes to analytical processes, investigates errors and manages corrective actions. It is also reasonable to ask how long records are retained, who can amend results, and whether changes to issued reports are logged. These controls help demonstrate that results have been managed responsibly if records are later reviewed during an audit, contract review or investigation.

Compare communication routes and technical support. Consider who will answer technical queries, whether queries are handled by suitably qualified staff, and how the laboratory records instructions or changes to a request. The ability to resolve an unclear sample reference or query a result through a documented process is more valuable than an informal assurance that support is available.

Review commercial terms in detail. Compare the complete cost rather than the headline price. Check whether charges apply for individual parameters, repeat analysis, rejected samples, amended requests, additional copies of records, courier arrangements or urgent work. Establish whether prices are fixed for the agreed service and whether any work may be passed to another laboratory. The quotation should make clear what is included so that different providers are being compared on an equivalent basis.

Consider consistency when choosing a long-term provider. For routine monitoring, comparable results depend on using a stable process, clear sample identification and consistent analytical arrangements. Changing laboratories can make trend review more difficult, particularly where reporting conventions or analytical capability differ. If a change is necessary, retain the previous records and document the reason, date and scope of the change.

Before appointing a laboratory, request its service information, technical scope, sample requirements, terms, example result documentation and escalation procedure. Then compare each provider against the same written criteria. The best choice is the laboratory that can produce technically credible, traceable and understandable results that fit the organisation’s risk management process, rather than the laboratory offering the lowest isolated test price.