Thames Water is among six water companies being sued for up to £1.5billion in a class action lawsuit over sewage discharges.
The suit claims that the water giants have underreported the number of sewage pollution incidents they are responsible for, which in turn led to the overcharging of customers.
The water companies involved - Severn Trent, Northumbrian, United Utilities, Anglian Water, Yorkshire Water and Thames Water - have denied the claims and have indicated they will robustly defend the claim.
The claim argues that underreporting of sewage incidents affected the price customers paid because the reports to the regulator Ofwat is a key factor in determining the price the company can charge.
It is being spearheaded by environmental consultant, Professor Carolyn Roberts.
“Water companies are required to report accurately pollution incidents as part of their legal duties and responsibilities, but it appears many such incidents go unreported,” she said.
“If these companies had correctly reported the number of pollution incidents, Ofwat would have applied performance penalties, reducing how much these companies could charge their customers.
“Instead, customers have been, and continue to be, overcharged, and England’s waterways continue to be polluted."
Leigh Day, the law firm representing the claimants, estimates that the case against Thames Water could be worth at least £159.1million if successful.
It also told the i that between them the companies may have to pay anywhere between £878million and £1.5billion in damages.
A Thames Water spokesperson said: “Thames Water is aware of the claims brought against it and other water and sewerage companies by Professor Roberts. Thames Water will defend the claims robustly.”
Thames Water, which serves around 11 million customers in London and the Home Counties, has faced repeated criticism over sewage discharges and concerns about service levels.
An urgent “do not drink” notice was issued to hundreds of Surrey homes following tap water tests last month.
The company said the advice was “precautionary” over “a possible deterioration” in the quality of drinking water in “some areas”, affecting around 100 homes in Bramley.
Separately, last month the utilities giant tested water samples after dozens of residents in south-east London reported sickness and diarrhoea.
However, it later said there had been “no failures from the Central Sydenham water zone,” and that the tap water was safe to drink.
