Proactive Investors - UK water companies have been found to have often discharged sewage into rivers and seas on dry days, which is illegal under environmental laws.
Three companies, Thames Water, Wessex Water and Southern Water, were found to have released sewage for a combined 3,500 hours on days when it was not raining in 2022, according to an investigation by the BBC.
Other companies may have also engaged in what is called 'dry spilling', but data was not available as there is an ongoing criminal investigation by the Environment Agency.
Water UK, the body that represents the industry, said the spills "should be investigated".
Three major water companies illegally discharged sewage hundreds of times last year on days when it was not raining, the BBC investigation suggests.
While water companies are allowed to release a certain amount of sewage into rivers and seas to ease the strain on sewers during heavy rain, they are not meant to do so when it is not raining.
The Environment Agency only recorded 115 cases of dry spilling in 2022 for the three companies, with an officer from the agency telling the BBC the agency was failing to identify and investigate dry spills due to having its budget cut by the government.
FTSE 100-listed water companies, United Utilities Group (LON:UU), Pennon Group (LON:PNN) and Severn Trent (LON:SVT) were not mentioned in the report but are far from able to boast clean bills of health when it comes to sewage spills.
They were among the UK water companies that apologised for sewage spills into rivers and the seaside earlier this year, promising to more than triple current levels of investment to £10 billion for sewer improvements, though they have said they want customers to pay for it.
United Utilities was responsible for more than 69,000 spills over 425,000 hours last year, while Severn Trent was responsible for 44,700 spillages, and Pennon subsidiary South West Water for 37,649.