Eleven of 17 water companies in England and Wales have been fined for missing their targets and will be forced to give customers millions off their bills.
At regular intervals, regulator Ofwat determines whether water firms have kept in line with industry standards on issues such as supply interruptions, pollution incidents and internal sewer flooding.
Breaches mean multi-million pound fines, which are then given back to customers in the form of bill reductions.
This year, however, with companies allowed to increase bills in line with CPIH inflation - which hit 8.6% in the 12 months to August - these reductions may be wiped out.
In total, £150m will be taken from companies and given back to customers in 2023 and 2024, with Thames Water and Southern Water the worst performing. They are being fined £51m and £28.3m respectively.
The best performing companies were Severn Trent Water in the South West and United Utilities in the North West. They will be permitted to generate an extra £62.9m and £24.1m in customer bills respectively.
Ofwat's assessment comes days after newly-appointed environment secretary Ranil Jayawardena forced water bosses to set out action on sewage being dumped in rivers and on beaches.
Several investigations have found raw sewage being illegally pumped into rivers and the sea around the UK.
"The volume of sewage spewed out by water companies is completely unacceptable, and the public have rightly shown their outrage," Mr Jayawardena said.
"In my first day in office, I told water chief executives that it is not good enough, and I have instructed them to write to me formally with a plan on how they are going to make significant improvements."
Water companies have also faced Britain's driest summer in years, with droughts resulting in long hosepipe bans.
David Black, the chief executive of Ofwat for England and Wales, added:
"When it comes to delivering for their customers, too many water companies are falling short.
"We expect companies to improve their performance every year; where they fail to do so, we will hold them to account.
"All water companies need to earn back the trust of customers and the public, and we will continue to challenge the sector to improve."
The yearly targets were set at the regulator's last price review in 2019 and will be in place until the next review in 2025.
How much is your water company being fined?
Affinity Water - £0.8m
Anglian Water - £8.5m
Dwr Cymru - £8m
Hafren Dyfrdwy - £0.4m
Northumbrian Water - £20.3m
SES Water - £0.3m
South East Water - £3.2m
South West Water - £13.3m
Southern Water - £28.3m
Thames Water - £51m
Yorkshire Water - £15.2
Firms allowed to charge more - and how much
Bristol Water - £0.6m
Portsmouth Water - £0.8m
Severn Trent Water - £62.9
South Staffs Water £3.3m
United Utilities - £24.1m
Wessex Water - £4.4m
(c) Sky News 2022: Eleven water companies fined and forced to give money off customers' bills
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