Question to the Department for Environment, Food and Rural Affairs:

To ask the Secretary of State for Environment, Food and Rural Affairs, how frequently drinking water is tested for compliance with (a) microbiological and (b) chemical safety standards.

The sampling frequency for drinking water is set out in Schedule 3 of The Water Supply (Water Quality) Regulations 2016 including which parameters are sampled at which point in the system, with some variation depending on factors such as treatment chemicals used, population served, etc.

There is also a requirement to monitor for anything else which may present a risk to health. The Drinking Water Inspectorate (DWI) ensures that these requirements are met by companies, and may on occasion increase the sampling frequency if a specific risk is under investigation.

The DWI published a report on 26 February 2025 recommending revisions to some parameters listed in the drinking water regulations. The report is the output of work by an advisory group of specialists both UK and internationally. Defra and the DWI will work together to consider potential regulatory updates to England’s drinking water quality legislation based on the recommendations.