Thames Water was fined £160,000 at Stratford Magistrates’ Court yesterday and additional costs of £79,839.68 for three separate drinking water offences in a case brought by the Drinking Water Inspectorate.

The fine is in respect of three offences arising from two events in February and July 2017 when there were failures in the disinfection of drinking water at Coppermills Water Treatment Works situated in Walthamstow, London.

The Inspectorate said that no consumers were harmed by either event but they were put at risk as disinfection of drinking water is a key public health measure. Coppermills Water Treatment Works is the sole supply to 728,000 consumers but contributes to 2 million consumers’ water supplies across the London area.

Disinfection at Coppermills Water Treatment Works is carried out by a number of treatment processes which include filtration of water through a sand bed and the controlled dosing of sodium hypochlorite (to disinfect) with electrically driven pumps.

Adequate disinfection relies on the careful control of these processes and water needs to be of low turbidity for disinfection to be fully effective.

In the first event, errors occurring in poorly planned electrical maintenance at the works led to the loss of control of the disinfection system and inadequately disinfected water entered supply. In the second event, disturbance in the flow of water across a sand filter raised turbidity (cloudiness) of the water and this affected the subsequent disinfection process.

The charges were brought under the Water Supply (Water quality) Regulations 2016.

Marcus Rink, Chief Inspector of Drinking Water commented:

“Whilst these events did not result in impact or harm to any consumers, Coppermills water treatment works suffered loss of control of key treatment processes on two occasions in 2017. Thames Water have experienced a number of similar incidents at other works which have led to repeated recommendations since 2014.”

“Recommendations on training, procedures, maintenance must be acted upon to reduce current and future risks. It is undoubtedly in the public interest to bring this prosecution for a strategic works which contributes to the supply of over two million consumers in Greater London.”

The Drinking Water Inspectorate investigates all drinking water quality events in England and Wales and will bring prosecutions if it believes that it has reliable evidence that an offence was committed, where the company does not have a defence that it took all reasonable steps and exercised all due diligence, and when such a prosecution is regarded as being in the public interest.