Have water companies really reduced storm overflow spills?

New data released yesterday by the Environment Agency shows a significant drop in the number of sewage spills from storm overflows. Spill numbers fell by 35% compared to 2024 with total spill duration also decreasing significantly – with many water companies seeing reductions of between 40% and 70%.  

The Environment Agency and campaigners have rightly pointed to the role of the weather in driving down spill numbers. But look behind the numbers and water companies are also making progress in cutting spills in their region.

Storm overflow spills happen because some of our sewers mix rainwater with wastewater from homes and businesses. This means when it rains heavily our sewers can quickly become overwhelmed and, to avoid sewage backing up into homes and businesses, we see storm overflows activate. So, broadly speaking, the more rain there is the more likely there are to be spills.

2025 was a lot drier than 2024. Across the whole year the UK received around 90% of its average annual rainfall in 2025. We also saw a very dry spring and summer which saw drought declared in parts of the country. 2024 meanwhile was very wet – the 13^th wettest since 1836. 

However, water companies are investing to end these spills regardless of the weather. A record £12 billion is being spent between 2025 and 2030 to cut spills in half. We’re already in the second year of this investment programme and there is intense activity up and down the country to reduce spills as quickly as possible.

In the northwest, United Utilities improved 400 storm overflows resulting in a 22% cut in spill numbers despite rainfall across the region being 101% of the historic average. On the other side of  the Pennines Yorkshire Water has invested £180 million to improve more than 100 storm overflows - reducing spills by almost 25%. A huge storm tank near Barnsley is also under construction. When finished the £5.3 million structure will hold 190m3 of water - the equivalent of 1,266 bathtubs!

Elsewhere, South West Water cut spills by 17% in 2025 despite the region receiving 62% more rain than England overall. On the other side of the country Anglian Water has removed 340 storm overflows from its network entirely, and set out detailed improvement plans for each of the company’s 1,442 storm overflows to significantly reduce discharges. Cross the River Severn and Welsh Water is looking to nature for solutions. The Pont-y-felin wetland uses a network of reedbeds and pools where native wetland plants will naturally filter pollutants and clean the excess water.

In total between 2025 and 2030 water companies are investing a massive £104 billion. As part of this investment water companies are building 10 new reservoirs, replacing thousands of miles of pipes and upgrading sewers.

We’ve recently launched a national campaign across England to show the progress water companies are making to deliver this investment. Check out the Big Upgrade campaign to find out what’s happening in your area.