Water supply companies in the UK have a duty under prime UK legislation to notify the Drinking Water Inspectorate of events affecting or potentially affecting the quality of drinking-water supplies. Under the same legislation, the Inspectorate has a duty to investigate each event. After assessing all of the information available, including companies' reports, the Inspectorate advises on the way in which the event was handled and whether any statutory requirements were contravened. If appropriate, a prosecution of the water company may be initiated. Copies of the assessment are sent to the water company, relevant local and health authorities, Ofwat (the economic regulator), the regional Consumer Council for Water and any other interested parties, including consumers who request it. Generic guidance may be issued to the industry on matters of wider concern.

This paper considers the role of the Inspectorate, the powers available to it and reporting arrangements. An overview is presented of events that occurred between 1990 and 2005 and common features are identified. Causes of different types of event are discussed. The importance of well-established contacts between the various interested parties involved in protecting public health is emphasised through discussion of example incidents.