Epsom and Ewell recorded the longest duration of storm-overflow discharges among seven constituencies examined in a new study of sewage spills across parts of South London and Surrey.
Research undertaken by Purley-based Drainage & Plumbing Ltd using official Environment Agency data identified 55 spills lasting a combined 801 hours during 2025 — equivalent to more than 33 days of continuous discharge.
Almost all the constituency’s total came from the storm overflow at Leatherhead Wastewater Treatment Works, which discharged into the River Mole 49 times for a combined 787 hours. A further four spills, lasting 12 hours, were recorded at the Manor Drive storm tanks discharging into the Hogsmill.
The geographical label refers to the parliamentary constituency in which an overflow is located and should not be confused with the boundaries of Epsom and Ewell Borough Council.
Epsom and Ewell did not have the greatest number of spills in the study. Mitcham and Morden recorded 125 and Reigate and Redhill 61. However, their combined discharge durations were considerably shorter, at 204 and 556 hours respectively.
Across all seven constituencies covered by the research, 250 spills lasting 1,578 hours were recorded during 2025. Epsom and Ewell therefore accounted for just over half of the total discharge time in the study.
The figures came from the Environment Agency’s Event Duration Monitoring returns. These record how often a monitored storm overflow operates and for how long, but not the volume of sewage released.
Storm overflows are intended to act as safety valves when rainwater and wastewater threaten to overwhelm combined sewer systems. They discharge diluted untreated sewage into rivers and other waterways to reduce the risk of sewage backing up into homes. Their frequency and duration have, however, become the subject of growing public and regulatory concern.
Flooding reaches Epsom homes and gardens
The same Drainage & Plumbing Ltd investigation examined Thames Water’s sewer-flooding register for the three financial years from 2022/23 to 2024/25.
Across the Epsom postcode districts, it identified 24 recorded incidents: 12 in KT19, seven in KT18 and five in KT17. Of the 420 incidents identified across all the areas examined, about two-thirds involved external flooding in gardens or yards, while just under one in five reached inside a home or business.
The information was obtained by the company under the Environmental Information Regulations. Thames Water said it did not yet hold a completed register identifying properties formally considered to be at risk of sewer flooding.
The flooding register only covers incidents attributed to Thames Water’s sewer network. It does not include flooding from private drains, burst water mains or surface water which never entered a sewer.
553 highway drainage reports
A separate investigation by the company found that Surrey County Council received 553 reports concerning blocked gullies, blocked highway drains or drainage flooding in Epsom and Ewell during the same three-year period.
Reports increased from 156 in 2022/23 to 229 in 2023/24 before falling to 168 in 2024/25. The latest figure was therefore 7.7 per cent higher than in the first year, although substantially below the intervening peak.
The borough accounted for three per cent of the 18,463 reports recorded across Surrey. Epsom itself generated 288 reports: 70 in 2022/23, 116 the following year and 102 in 2024/25.
The countywide information was obtained from Surrey County Council through a Freedom of Information request submitted by Nima Fazlipour, director of Drainage & Plumbing Ltd. The company said it checked the 18,463 individual records against the Council’s annual and electoral-division summaries.
The figures count reports made by members of the public rather than confirmed blockages. They do not show how many reports concerned the same problem, how many resulted in repair work or how quickly the Council responded. Surrey’s released spreadsheets did not include gully-cleaning totals or dates on which cases were resolved.
A road gully is the grated opening beside a kerb which carries rainwater away from the highway. Its underground pot can become filled with silt, fallen leaves and road debris, leaving water standing on the carriageway after rain.
Highway gullies are generally maintained by the county council, while public sewers are the responsibility of Thames Water. Drains within private property boundaries ordinarily fall to the property owner.
MP says infrastructure is failing
Helen Maguire, Liberal Democrat MP for Epsom and Ewell, has accused Thames Water of failing to invest sufficiently in its ageing infrastructure.
Her intervention came as Thames Water customers remained subject to a hosepipe ban introduced following prolonged dry weather, heatwaves, low rainfall and unusually high demand.
Figures analysed by the House of Commons Library and the Liberal Democrats indicate that Thames Water lost an average of 569.1 million litres of treated water a day through leaks during 2024/25. That is equivalent to approximately 228 Olympic-sized swimming pools every day.
Those leakage figures apply across Thames Water’s network and should not be read as losses occurring within Epsom and Ewell alone. They nevertheless add to concerns about the resilience of the company’s infrastructure as it attempts to manage both periods of drought and the overloading of sewers during heavy rainfall.
Ms Maguire said she had written to Thames Water seeking a meeting about its preparations for increasingly extreme weather and how it intends to make the water network more resilient.
She said: “Thames Water needs to urgently get its house in order. They have got away with their negligent handling of our water infrastructure for far too long. It’s simply not good enough.
“Whilst residents in Epsom and Ewell have to face a hosepipe ban as well as continuing increasing bills, Thames Water continues to fail. Thames Water must stop rewarding their unaccountable bosses with bonuses and start investing in fixing their infrastructure so we can avoid this happening time after time.”
Ms Maguire also called for customer payments to be reinvested in stopping leaks and preventing sewage discharges, supporting her party’s proposal for water companies to be placed under a mutual ownership model.
The Government has already announced that Ofwat will be abolished and its functions combined with water-related responsibilities currently divided between the Environment Agency, Natural England and the Drinking Water Inspectorate. The existing regulators retain their legal powers until the new regulator is established.
Different drains, common concern
The highway gully, sewage overflow, sewer-flooding and clean-water leakage figures describe different parts of the water and drainage system and should not be treated as one dataset.
Taken together, however, they illustrate the competing pressures placed on local infrastructure: too little available water during prolonged dry weather, leakage from the supply network, road flooding when surface drainage becomes blocked and sewage discharges when combined sewers are overwhelmed.
Drainage & Plumbing Ltd brought its two investigations to the attention of the Epsom and Ewell Times. The company, based in Brighton Road, Purley, provides commercial drainage services across Surrey and South London.
EET acknowledges the public-interest work of Mr Fazlipour and the company in obtaining, checking and publishing the official information.
The full datasets and methodology can be examined in the company’s reports on sewage spills and sewer flooding and blocked highway gullies.

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Image: River Mole in Leatherhead – geograph.org.uk Nigel Cox
















