Thames Water urges Gerrards Cross residents to help trace the source of industrial oil pollution infiltrating its sewer infrastructure
Substance in primary settling tank
- First identified in 2024 and reported to the Environment Agency, the source of the ongoing oil pollution affecting Thames Water’s sewers and the ecologically rare River Misbourne remains unknown.
- Thames Water is committed to ensuring industrial discharges into its sewers do not impact its customers, assets and the environment.
- Under the Water Industry Act 1991 and the Environmental Permitting Regulations 2016, discharging trade effluent into public sewers without a valid trade effluent consent, or causing a water discharge event without a permit is a criminal offence.
Thames Water is appealing to residents and businesses in Gerrards Cross to help identify who is polluting sewers with industrial oil and potentially putting the River Misbourne at risk.
The issue, which first occurred in 2024, has been reported to the Environment Agency and Thames Water continues to work with the regulator to identify the source and ensure compliance.
Tracing where the oil is being poured into the sewer has proven difficult as it can only be detected further down the network. Thames Water is appealing for anyone who thinks they know the location or has seen illegal discharging to call the 24/7 pollution hotline on 0800 807060 or file a report online.
Businesses are required to treat potentially hazardous waste prior to discharging it into the sewer network and must only do so in compliance with a valid trade effluent consent. Neglecting to do this has the potential to cause blockages, sewer flooding and environmental pollution.
In the case of the unknown source in the Gerrards Cross area – the potential damage is two pronged:
- Environmental damage: the River Misbourne, home to diverse species of flora and fauna is highly vulnerable to contamination. Its chalk streams are among the rarest in the world, making protection essential.
- Infrastructure impact: industrial oil can corrode or block critical assets at local sewage treatment works Sewage Treatment Works, risking service disruption and sewer flooding for customers.
This serves as a stark reminder of why businesses should always be mindful of how they discard hazardous waste, whether fats, oils, grease or other biohazards that can cause damage to both Thames Water’s infrastructure and the environment.
Stephen Crabb, Head of Waste Operations Home Counties, said: “Sewer abuse is part of the everyday challenge we face to keep our sewers flowing in order to remove and treat customers’ wastewater.
“This recent occurrence in Gerrards Cross is not only a crime but it also highlights that when it comes to safeguarding river health, there are other actors at play, and we cannot address this alone. Protecting sensitive chalk streams like the River Misbourne requires a shared effort across the community.
“While we continue to do all we can to identify those responsible, we will always work with individuals and companies to educate them on the impacts of sewer abuse. However, we may take legal action where appropriate to safeguard our assets as well as rivers and the communities that depend on them.”
Thames Water continues to take action to improve the health of rivers across its catchment areas as a key priority.
Over the next five years, it is delivering the most significant upgrade to its wastewater network in 150 years, including increased treatment capacity, reduced storm discharges and new nutrient reduction schemes.
In 2024, Thames Water ordered two food companies to pay a combined total of £265,500 after they disposed of excessive amounts of chemicals, food solids and fats into the sewers in North West London.
Sewer abuse is a major issue for water companies. Every year, Thames Water removes 75,000 blockages from its sewers at a cost of £40 million per year, a cost that is ultimately passed on to customers.
Residents can report incidents via the 24/7 pollution hotline: 0800 807060, or by filing a report online.
Notes to editors:
- Summary of impact that industrial oil can have on Thames Water’s infrastructure:
|
Impact Area |
What happens |
Why it matters |
|
Pipe blockages and reduced flow |
Oil solidifies and forms into fatbergs causing blockages and sewer flooding |
Causes reduced hydraulic capacity, backups and increases chances of sewer discharges |
|
Mechanical and equipment damage |
Oil coats inlet screens (responsible for filtering solids in the treatment process) and other mechanical parts |
Leads to reduced efficiency, increased maintenance costs (ultimately passed on to customers) and premature equipment failure |
|
Higher sludge production |
Excess oil increases sludge volume and anaerobic conditions |
Raises disposal costs and causes odour issues |
|
Effluent quality deterioration |
Oil interferes with physical and biological steps, increasing Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) and hydrocarbons in effluent water |
Can be harmful to wildlife and cause long-term ecological harm |
|
Operational disruption and cost |
Higher energy use, more chemical dosing may be required in the pretreatment process |
Increases operating costs, downtime and risk of penalties for effluent violations |