Water testing labs for organisations: checking accreditation and method scope before you send a sample, and what the report must show

What to establish before sending a sample

1. Certification and the accredited scope. Ask which programme certifies the laboratory, for which analytes, by which methods, and ask for the current scope document. A laboratory may be entirely competent and still outside scope for your particular analyte, and the certificate is what a regulator reads.
2. Methods by designation. Regulatory testing specifies methods by published designation, and results are only comparable when the method is the same. Ask which method will be used for each analyte rather than accepting a general capability statement.
3. Reporting limits in your matrix. The limit the laboratory can report to depends on the matrix as well as the method, and a limit above your compliance threshold makes the result useless. Confirm the achievable reporting limit for your sample type against the threshold you must demonstrate.
4. Sampling, containers and hold times. Many analytes require specific containers, preservatives, filling technique and a hold time measured in hours. The laboratory should supply containers and written instructions, and a sample that misses a hold time is not salvageable however good the laboratory is.
5. Chain of custody and turnaround. For anything with a compliance or legal consequence, the chain of custody form is part of the result. Establish the turnaround for standard and expedited work and what happens if a sample fails a quality check on arrival.

Reading the report

A report should state the method, the reporting limit, the result with units, the sampling and receipt dates and times, and the quality control outcomes for the batch. A bare number against a threshold is not an interpretable result.

Ask what the laboratory does when a quality control check fails and whether affected results are flagged. A laboratory that explains this readily is showing you its quality system working.

Where this hub stops

This page covers organisations choosing an accredited laboratory for compliance, process or environmental testing. Consumer home water test kits are a different buyer and a different market and are not covered here.

For sampling plans and interpretation against a specific regulatory limit, the authority that set the limit publishes the requirement, and the laboratory itself is usually willing to advise on sampling for the analytes it runs.

Common questions

How do I check a water testing lab's accreditation?

Ask for the current scope document naming the analytes and methods it is certified for, and confirm your analyte and method appear on it. Competence and accredited scope are not the same thing.

Why does the method designation matter?

Regulatory testing specifies methods by published designation, and results from different methods are not necessarily comparable. Ask which method will be used for each analyte.

What are hold times?

The maximum period between sampling and analysis for a given analyte, often only hours, alongside container and preservative requirements. A sample analysed outside its hold time cannot be rescued.

What should a water test report contain?

The method, the reporting limit, the result with units, sampling and receipt dates and times, and the batch quality control outcomes with any affected results flagged.

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