Water companies are permitted to release sewage into rivers and seas in exceptional circumstances such as heavy rain

Credit: Paul Quayle/Alamy Stock Photo

Water companies released sewage during the record heatwave of 2022,despite rules that spills should only happen in extreme wet weather,according to data.

Data on the start and stop times of spills from combined sewer overflows,seen by the BBC,suggest sewage may have been spilled during dry weather about 6,000 times in 2022.

Water companies are permitted to release sewage into rivers and seas in exceptional circumstances such as heavy rain,when there is a risk that the system may become overwhelmed and sewage could back up into homes.

Spills outside those circumstances could be illegal and should be reported to the Environment Agency for investigation.

Analysis by the BBC of data provided by the Environment Agency suggests dry spills may have occurred on more than 200 days in 2022.

This includes days during the record heatwave that summer,which was the fifth driest since the 1890s.

Spills during dry weather are particularly concerning because of the reduced dilution of the sewage,which means it is likely to have a bigger impact on the aquatic environment,and the risk to people using the water for swimming and sports.

Helen Wakeham from the Environment Agency told the BBC that the results were unsurprising,given the poor level of investment by water companies.

The water companies disputed the findings,which they said were based on incomplete data and flawed analysis.

The BBC said the main reason given for disputing the figures was that monitors malfunctioned and incorrectly recorded spills.

Companies claim data ‘unvalidated’

Yorkshire Water and Northumbrian Water said that they did not believe the BBC’s findings were a true reflection of dry discharge numbers.

United Utilities said: “The information you have received from the Environment Agency reflects unvalidated,raw signals and not validated start/stop times.”

Anglian Water told the BBC that the data was unreliable because of possible monitor malfunctions and also said the methodology was flawed.

A Thames Water spokesman said: “There are a number of methodologies for defining and calculating why and how dry day spills occur.

“We regard all discharges of untreated sewage as unacceptable,and we have planned investment in our sewage treatment works to reduce the need for untreated discharges.”

A Wessex Water spokesman said: “Naturally occurring groundwater can enter sewers,often from private pipes and in dry weather,which can cause overflows to operate for days or even months.

“We agree overflows are outdated so we’re investing £3 million a month to help reduce how often they automatically operate.”

A Southern Water spokesman said: “In areas with high levels of residual groundwater,spills can happen outside of periods of rainfall. Without these releases – made up almost entirely of groundwater – homes and communities would be flooded.

“Combatting these groundwater spills is a key part of our £1.5 billion clean rivers and seas plan,which is designed to drastically reduce all storm overflows across our region by 2030.”