Pollution incident reduction

We cover a vast area; our 110,000km sewer network could stretch 3 times around the Earth. This network transports 4.7 billion litres of wastewater daily from our 16 million customers. That's enough to fill nearly 2,000 Olympic-sized swimming pools.

We face several challenges. Our pipes and other equipment are ageing, and our region’s population is expected to grow by 2.5 million by 2050. Additionally, climate change is bringing more extreme weather, including heatwaves and intense rainfall.

In this tough environment, we're proud of our performance improvements over the last year. However, we know there's still a long way to go and it will take years to reach our goals because of the level of investment required across our hundreds of sites. In 2025**, total pollution dropped by 18% (to 386 incidents from 470) compared to 2024. Serious pollution fell by 27% (to 24 incidents from 33). Also, pollution numbers at wastewater pumping stations have been the lowest across the industry for 2 years in a row.

**2025 pollution data was not finalised at publication due to ongoing regulatory appeals. Final numbers are expected to be lower.

The biggest cause of pollution is blockages, which restrict flow in pipes and cause sewage to come out of the network where it shouldn’t. Most blockages are caused by people putting things down the toilet, sink, drain or even straight into manholes which they shouldn’t. This includes wet wipes, fats, oils and greases, concrete, and even a fridge freezer last year! The best way to avoid blockages is for everyone to follow our advice: bin it, don’t block it!

Other pollution causes include when our equipment doesn’t work as it should, like sewer defects or pump failures. Heavy rain and groundwater can overwhelm our sewer’s capacity, which we call hydraulic overload, although most of these discharges are heavily diluted. Sometimes, other people cause us issues too (we call this third-party), for example, people damaging our pipes. Another instance of third party issues is misconnections, where domestic appliances and toilets are incorrectly connected to the surface water sewer, which results in wastewater entering the environment without being treated.

From 2026, we expect pollution numbers to increase dramatically across the industry, in line with our collective ambition to be more transparent. This is because we now have more monitoring to tell us when things go wrong and the Environment Agency is changing the way it categorises pollution incidents. The new regulations mean some incidents will now count as pollution when they didn’t before. Because of these changes, incident numbers from 2025 and 2026 cannot be easily compared. The Environment Agency has also recognised this by agreeing to exclude pollutions from their Environmental Performance Assessment reports in 2026 and 2027.