Water customers in England and Wales may be owed £163m for sewage spills, corporate wrongdoing researchers claim.
Water firms charge customers to treat sewage, but instead have been widely discharging it in to rivers and on to beaches, researchers from Fideres said.
The firms have not invested enough, leading to an “excessively low quality service”, the researchers said.
However, a water industry body said firms were putting in place a £56bn programme to tackle spills.
Water firms have been under pressure to clean up their act after discharging sewage in to rivers and the sea 400,000 times in 2020.