Bills could rise after water suppliers in England said they were ready to spend £10bn on tackling sewage spills.
The privately owned companies have apologised for the amount of contaminated water being discharged into rivers and seas, amid mounting public anger over the practice.
Some campaigners have cautiously welcomed the move, but others say firms are shifting the cost on to billpayers.
The industry paid out £1.4bn to shareholders in 2022.
Musician and environmental campaigner Feargal Sharkey called it a "half apology" that was another attempt to extract more money from customers.
"What I am actually hearing is no apology for the fact we have paid them for a service we haven't got, they are now suggesting we pay them a second time for a service we haven't had," he told BBC Radio 4's Today programme.
"We should have an apology for the suggestion they are going to put bills up by £10bn for their incompetence and their greed. This is nothing to celebrate."
Companies are sometimes allowed to spill sewage into open water following heavy rainfall to prevent the system becoming overloaded and backing up into people's homes.
But campaigners have long said these spills are happening too often. In 2022, raw sewage was dumped into rivers and seas for 1.75 million hours - or 825 times a day on average.
Untreated sewage contains bacteria such as E.coli and viruses like hepatitis, that can be harmful to animals and humans. Swimming in water where untreated sewage is discharged can lead to serious illnesses such as stomach bugs, which may cause diarrhoea and vomiting, as well as respiratory, skin, ear and eye infections.
Wildlife including fish and insects can also experience kidney issues and die from sewage pollution.
Water UK, the body which represents England's nine water and sewage companies, apologised on behalf of the industry for not "acting quickly enough".
Ruth Kelly, the organisation's chair, told BBC News: "We're sorry about the upset and the anger from the fact that there have been overspills of untreated sewage onto beaches and into rivers over the past few years.
"We're sorry that we didn't act sooner, but we get it."