Deviating samples

Deviating samples

Following guidance, issued by UKAS, we have strengthened our focus on the handling of deviating samples. 

What is a deviating sample?

UKAS guidance states that samples will be labelled as deviating if:

  • no time or date of sampling has been supplied
  • the sample is in the incorrect container or not been correctly preserved
  • the container has been incorrectly filled
  • the sample age exceeds the stability time.

If a sample is deviating, the validity of the results is in doubt.  Received samples will be assessed at the laboratory, for each analysis. This will include the container(s), and its filling, preservation, age of sample, and all correct information supplied.

Samples that do not conform to these requirements will be highlighted as deviating on the reported analysis, or in extreme cases cancelled.

Stability times have been established from detailed laboratory tests or recognised sources (principally ISO-5667-3).

A stability time is the maximum time for stability for that determinand, in that matrix (sample type). A listing is available on request - please email

Gross deviations will be cancelled, such as, a bacteriological sample received in a non-sterile bottle.

What will you see?

The reported analysis will indicate when a test is deviating.

The following are examples of what may appear on the analysis report.

  • If no date or time is supplied: Unknown sample age, results may be affected.
  • If a sample is received in an incorrect container: Incorrect container, results may be affected.
  • If the stability time is exceeded at registration: Stability time exceeded, results may be affected.
  • If a determinand exceeds its stability time at analysis: Stability time breached within laboratory, results may be affected.

In submitting samples to the Wessex Water Scientific Laboratory, you are accepting the requirements to follow these guidelines.

All deviating tests are analysed with the understanding that they will be paid for within our normal terms and conditions.

Deviating samples bottle examples

How you can help

Please follow the sampling guidelines.

To enable us to analyse samples within the stability time, please ensure samples arrive at the laboratory on the same day as sampling.

  • Always provide correct sampling details, such as the time and date of sampling.
  • Use correct containers for sampling, and fill according to requirements, see lists below.
  • If preservative is required, ensure that samples are preserved at the time of sampling.

All samples (except soils and Legionella) should be refrigerated after sampling. 

This will minimise the deviations you receive, and ensure the validity of your results.