# 9.10.4 Measurement uncertainty There is an inherent level of uncertainty associated with the measurement of water quality characteristics, in addition to the uncertainty arising from sampling. This inherent uncertainty arises from a number of sources, but it primarily relates to the accuracy of the laboratory equipment used to produce a result, and various measurement errors that may be introduced through the analytical process. In some cases, the level of uncertainty will be insignificant relative to the quoted result; in other cases, however, it can be quite significant. Under the ISO Standard used by NATA for accreditation, *AS ISO/IEC 17025—2005 – General Requirements for the Competence of Testing and Calibration Laboratories*, laboratories are required to estimate the uncertainty associated with the results they produce (known as the measurement uncertainty). Upon request, NATA-accredited laboratories are required to provide the measurement uncertainty (MU) associated with a particular analytical result (x), which should be expressed by the laboratory as either x ± MU, or as a percentage of x, or in any other manner accepted by the relevant accreditation body. Organisations performing water quality testing are encouraged to request that their laboratories provide MU data as part of their analytical results reporting. This will promote an appreciation of the variability in the analytical data being received. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://guidelines.nhmrc.gov.au/australian-drinking-water-guidelines/part-3/chapter-9/9.10-reliability-of-monitoring-data/9.10.4-measurement-uncertainty.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.