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Less than 12 per cent of the sewage network in England and Wales was built in the 19th century, undermining water industry claims that outflows of raw effluent and storm water are a result of antiquated Victorian infrastructure.
The majority of the network was instead built in the years before privatisation, with approximately a fifth constructed during the 1960s and 1970s, according to data analysed by consultancy Arup and campaigners Windrush Against Sewage Pollution.
Professor Peter Hammond, data researcher for Wasp and former professor of computational biology at University College London, said the findings debunked the argument from water companies and government that sewage outflows could be blamed on the Victorian waste water networks.
“Victorian sewers constitute a minor proportion of the sewer network and cannot be blamed for the toxic mix of untreated human waste and road surface run-off polluting our inland and coastal waters,” said Hammond, who has appeared at several parliamentary hearings on water.
“The disparity of infrastructure investment before and since privatisation must surely bear the brunt of blame,” he added.
The analysis contradicts the argument often made by the water industry and government that the privatised water companies are releasing raw sewage into coastal waters and rivers partly as a result of having inherited infrastructure that was built in the Victorian era, which ended in 1901.
As recently as April Thérèse Coffey, the secretary of state for environment, food and rural affairs, said: “Sewage overflows stem from our principally Victorian infrastructure”.
In July 2023 Water UK, the trade association, said: “The industry is strongly committed to accelerating the pace of improvement, including with a £10bn overhaul of our Victorian sewage system to transform our rivers and seas.”
However, Hammond’s analysis found no evidence to suggest that Victorian sewer networks were more likely to be involved in spills of untreated sewage. “More likely it is the lack of maintenance and investment,” he said.
Financial Times analysis of data from Ofwat, the regulator, has found that investment in sewage infrastructure has fallen while the population has grown. Spending on wastewater infrastructure — including pipes — has fallen in real terms from an annual average of £3bn in the 1990s to £2.7bn in the 2020s so far, despite a 16 per cent increase in the population in the past two decades.
The result is a sewerage system that is often overwhelmed, causing raw effluent to be discharged through the network’s 16,563 combined sewer overflow pipes, which are designed to be used only during periods of heavy rain.
Dieter Helm, a professor of economics at Oxford university, said water companies, regulators and politicians “should stop blaming the problem on what the Victorians did a century and a half ago”.
“The data shows there has been inadequate capital maintenance and companies have not been kept up to the mark,” he said. “What we need now is a new Victorian mindset — and to urgently get on with investment now.”
After being privatised without debt in 1989, and given a £1.5bn government handout to make improvements to the network, water companies had ramped up £60bn in borrowing by March 2022 and paid out more than £70bn in dividends while presiding over leakage and pollution failures, including unknown quantities of untreated sewage pouring into coastal waters and rivers.
Beaches and rivers have been closed to swimming for several days this summer, while last week at least 57 people fell ill with diarrhoea and vomiting after a World Triathlon Championship Series event off Roker Beach in Sunderland. The UK Health Security Agency has confirmed that it is investigating whether sewage was to blame.
Although companies also often blame unpredictable weather and climate change for causing more frequent untreated sewage overflows, a study by Imperial College London this year found that by far the biggest problem was insufficient capacity at wastewater treatment plants, which meant they were releasing sewage into waterways even during dry periods.
The quantity of raw sewage flowing into rivers and coastal waters remains unknown. Although the government has required that all combined sewer overflows have monitors installed to record discharges by the end of this year, they record only when they occur and not the volume released.
Water UK said: “England has 100,000 kilometres of older ‘combined’ sewers with more than 15,000 storm overflows. A large proportion of this combined sewer goes back to the Victorian era. Companies have acknowledged that they haven’t done enough to upgrade this part of the network but are proposing to spend more than £10bn to put it right.”
Defra said: “We are clear that water companies must deliver more and better for the environment and their customers.”
Ofwat declined to comment.