Proficiency testing

Proficiency tests are an important instrument for the harmonisation of (environmental) measurements; they allow laboratories to compare their results with those of other laboratories. For more than 30 years, KWR has conducted proficiency tests for a variety of laboratories, such as environmental labs, water labs, as well as those of waterboards, hospitals and food-processing companies. Our proficiency tests are accredited by the Dutch Accreditation Council (nr. R005).

Every year, KWR sets up an annual programme for organic, inorganic and microbiological proficiency testing. This enables laboratories to regularly test and evaluate their procedures based on the (routine) samples. To give the laboratories good insight into their own performance in daily practice, KWR provides them with samples which are made of practice water matrices. The samples are made from drinking water, surface water, groundwater, wastewater and bathing water; the participating laboratories themselves decide which analytical method(s) to apply.

Proficiency test samples

Proficiency test samples

Features of KWR’s proficiency testing

  • Every year, our proficiency testing involves about 45 organic, inorganic and microbiological laboratory-evaluation tests for various types of water and more than 100 parameters.
  • The tests are based on the Youden technique, which allows the nature (random/systematic) of any deviations to be determined.
  • The results are presented in both tabular and graphic form.
  • The tests provide information about the (performances of) the analytical methods used by the participants, which makes it easier for them to interpret their scores.
  • The proficiency tests produce a value assessment in the form of a group performance score, which provides a quick impression of the quality of the results achieved for separate parameters, and how these develop over time. The results are assessed for different statistical indicators. In general, a single score is given per matrix and per parameter.
  • By giving a z-score, the proficiency tests assess the individual performance of each laboratory against the group average and, for chemical proficiency tests, against the theoretical value as well.
Collecting proficiency test samples in the laboratory

Collecting proficiency test samples in the laboratory


The proficiency test results are reported under random numbers to guarantee their anonymity. The report also provides insight into the analytical methods applied, which allows each participant to determine whether any deviations are caused by the methods used or have some other origin.

Tailored proficiency testing

In addition to the proficiency tests that KWR organises as part of the annual programme, tailor-made proficiency tests are also available. KWR has years of experience with the organisation of proficiency testing for quality assurance with new methods (such as RT-PCR), alternative validation methods and for the analysis of new substances. In addition, KWR also organises and participates in various proficiency tests in the NORMAN network. Our experts are available to discuss the possibilities with you.