Two of Thames Water’s largest contributors to discharges in East Berkshire have reduced their activity by around three-quarters over the past year, new data shows.

Environment Agency (EA) figures over the last five years reveal a sharp drop in storm overflow activity in 2025, following a peak in 2024 when many sites recorded their highest levels of spills.

Across nine monitored locations in South Buckinghamshire and East Berkshire, five sites – Maidenhead, Hambleden, Iver, Taplow and White Waltham – recorded zero spills in 2025.

However, Thames Water’s sewage treatment works in Slough and Windsor remain outliers and recorded a combined 48 spills totalling more than 500 hours in the same year.

Slough and Windsor recorded the highest number of discharges over the five-year period.

Windsor’s figures rose from 70 spills in 2021 to a peak of 133 in 2024, before falling to 34 in 2025 – a reduction of around 74 per cent year-on-year.

A similar pattern could be seen in total discharge time, which more than doubled between 2022 and 2024 before dropping by more than 80 per cent last year.

Slough showed a more pronounced increase as, after recording just eight spills in 2022, incidents rose to 32 in 2023 and more than doubled again to 70 in 2024.

This fell back to 14 in 2025 – an 80 per cent decrease.

Total discharge duration in Slough was significantly higher than in the other sites analysed in the dataset.

Although the Windsor and Slough sites saw a reduction in 2025, they still accounted for the majority of discharges in the area.

Other locations recorded lower rates, such as at Little Marlow, which recorded 27 spills lasting more than 460 hours in 2021.

This dropped to two spills totalling 10 hours in 2025 – a reduction of more than 90 per cent.

Maidenhead recorded two discharges totalling 16.25 hours in 2024, which fell to zero in 2025.

It also recorded no spills in 2022 and 2023.

White Waltham also saw comparatively lower levels of discharges; after recording three spills in 2021 and two in 2024, it reported no discharges in 2022, 2023 or 2025.

Taplow recorded three spills in 2021, worth more than two hours in duration, but did not record any further activity for the following four years.

The data highlights 2024 as an exceptional year, coinciding with heavy rainfall in February which caused widespread flooding in the Thames Valley, described as the ‘worst in a decade’.

A Thames Water spokesperson said: “The latest EDM [monitoring] returns show discharge events were around three times lower than the previous year with shorter spill durations.

"Although we acknowledge this is in part due to reduced rainfall in 2025, we are encouraged that we are seeing early signs of progress from the operational and capital investment we have been making.

“Our infrastructure requires significant investment to meet our commitment to reducing discharge frequency and duration.

"That is why over the next five years we are delivering the biggest upgrade to our wastewater network in 150 years, including increased treatment capacity, reduced storm discharges and introducing new nutrient reduction schemes.

"This includes upgrades to our Slough Sewage Treatment Works and Windsor Sewage Treatment Works by expanding the sites capacity to treat sewage.

“Transparency is at the heart of what we do, and in January 2023 we were the first water company to publish a real-time EDM data map on our website, before it became a legal requirement to do so.”