The Guardian: 30 water treatment works released 11bn litres of raw sewage in a year, study suggests
“Eleven billion litres of raw sewage were discharged from a sample of 30 water company treatment works in one year, new research suggests.
The study aimed to reveal the volume of discharged effluent released from storm overflows by water firms. Companies are not forced to reveal the volume of raw sewage released during discharges. They are only required by regulators to provide data on the number of discharges and the length of time they lasted.
Recommendations by MPs on the environmental audit committee that volume monitors be installed by water companies have so far been rejected by ministers.
In a study of 30 treatment works in 2020 run by nine of the 10 water and sewerage companies in England and Wales, the volume of raw sewage discharged was estimated at 11bn litres – or the equivalent volume to 4,352 Olympic pools.
Prof Peter Hammond, a mathematician who analyses data on sewage discharges, carried out the research. He has previously given evidence to MPs to reveal that the scale of illegal discharges of raw sewage by water companies is 10 times higher than official data suggests.
Hammond said it was vital to establish the volume of sewage discharges by water companies. He said his research suggested the government’s target to reduce raw sewage releases to 20 per year by 2025 was not robust because there was no requirement to reveal the volume of raw sewage discharged for each release.
“There is still no data readily available showing the volume of untreated sewage discharges,” he said. “Water companies have some idea, but the regulators [Ofwat and the environment agencies in England and Wales] and the government [the Department for Environment, Food and Rural Affairs] probably have no idea. Sewage detritus in rivers, on beaches and in seas offers clues but may not reflect the volume of discharges.
“So what is the potential discharge volume for 20 spills per overflow per year?”
Of the 30 treatment works analysed, only one – Mogden sewage treatment works in west London – has volume monitors fitted. In 2020, Mogden, which serves more than 2 million people, released a volume of raw sewage equivalent to 2,768 Olympic pools.
The average volume of sewage discharged per spill from the other 29 treatment plants in 2020 was 1.3 Olympic pools. The government target of 20 spills per year by 2025 would therefore still involve huge volumes of untreated sewage, according to the analysis.
“Even if the government’s storm overflow discharges reduction plan target of 20 spills per overflow per year were to be achieved, some treatment works could still discharge a volume equivalent to 26 Olympic pools of untreated sewage annually,” Hammond said.
Measuring the volume of discharges was vital to establish the environmental impact of them upon rivers, he said. “Individual rivers receive direct, simultaneous discharges of untreated sewage from multiple storm overflows on their journey from source to sea,” Hammond said. “So, during longer spills, the lower reaches of a river may already be polluted from upstream discharges when yet more overflows downstream discharge untreated sewage.”
