Our main job is to check that the water companies in England and Wales supply safe drinking water that is acceptable to consumers and meets the standards set down in law.

The DWI provides a wealth of information on drinking water quality for England and Wales. Most of the information requested is already publically available through the website and published reports.

If you have any information requests for the DWI, please contact us by email dwi.enquiries@defra.gov.uk or by telephoning the enquiry line at 0330 041 6501.

Every day tap water is tested by the water companies. Our inspectors independently check these tests and audit water company laboratories. If any one of the millions of tests each year fails the standards then our inspectors use their powers to require the water company to make the necessary improvements to drinking water quality. Our inspectors go out on site to check that improvement work is completed on time. They also inspect that the aspects of water operations which ensure drinking water is safe at all times.

Very occasionally things go wrong. When this happens it is our job to investigate the operational incident and provide an independent report of the cause with recommendations on how to prevent similar events from happening again. Sometimes our investigations of incidents lead to a water company being prosecuted. In addition when a water company fails to resolve a drinking water quality complaint then the consumer can come to us for help.

Drinking water standards

The legal standards for drinking water are set down in national regulations (for England and for Wales), which originally came from European law. The health-based standards are based on expert global opinion documented in World Health Organisation guidelines. These standards are very strict. We also have some additional national standards set to maintain the high quality of drinking water in England and Wales.

Our powers and duties

Our Chief Inspector of Drinking Water is appointed by the Secretary of State for Environment, Food and Rural Affairs and Welsh Ministers and acts independently on behalf of these authorities. Certain powers are vested directly in the Chief Inspector of Drinking Water. The legislation is set out in the Water Industry Act 1991 as amended by the Water Act 2003. Equivalent regulators exist in Scotland and Northern Ireland.

WHO Collaborating Centre for Drinking Water Safety

The Inspectorate is a World Health Organisation Collaborating Centre for Drinking Water Safety, and has been redesignated for a further four years to January 2026. This recognises our knowledge of risk based regulation in the field of drinking water quality and supply, our adoption of drinking water safety plans, and our work on small supplies risk assessments.

An important function of our collaborating centre role is to provide support to WHO Europe. This is in the form of regulatory and technical knowledge exchange, workshops, training programmes, benchmarking projects and research studies. We work with WHO to build capacity within countries to improve drinking water regulation, and to share our experience, technical guidance and risk based approach.

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