Storm Henk brings Thames Water’s worst day of sewage spills since records began

Storm Henk brought the worst day of sewage discharges into rivers in parts of south-east England since public records began as Thames Water’s infrastructure came under extreme pressure.

An analysis of data published by Thames Water shows that it was simultaneously discharging waste from nearly 300 separate locations on Thursday 4 January. This is the highest number recorded since the firm started publishing its data last year.

It comes after Storm Henk brought heavy rain and major flooding to parts of the UK.

Thames Water has apologised for the discharges, which it said were made worse as the storm “came at a time when the ground was already saturated from a long period of wet weather”.

Like other water companies, the water firm discharges untreated sewage into rivers from points known as combined sewer overflows (CSOs) during periods of heavy rainfall.

This is to prevent their pipe systems from becoming overwhelmed and sewage backing up into people’s homes.

But firms have come under intense criticism for the amount of sewage they are dumping into rivers, lakes and coastal waters.

In January last year Thames Water became the first water company to publish real time data of when they were discharging waste through CSOs.

Dr Alex Lipp, a scientist at the University of Oxford, has tracked the data released by Thames Water over the past year and co-created a map showing the impact the spills are having on the region’s rivers.

According to the data, Thames Water reached a peak of 295 separate discharges at 9pm on Thursday 4 January, when London and the south east were being battered by heavy rain and flooding.

This is the single highest number of simultaneous discharges recorded since Thames Water started publishing its data in January last year.

According to Dr Lipp, 357 of Thames Water’s CSOs discharged sewage during a 48 hour period when Storm Henk battered the region, which is 83 per cent of the total number of CSOs operated by the water company.

“Pretty much everywhere in the catchment would be impacted by this,” Dr Lipp said. “These overflows discharge raw sewage and that contains a variety of things which we know to have negative impacts on river health.”

He said sewage is full of phosphates and nitrates that contribute to pollution, while studies have also found human waste to include things such as pharmaceuticals and illegal drugs that have a detrimental impact on river health.

While Thames Water is currently the only water company to provide real time data on sewage discharges, Dr Lipp warned a “similar thing is happening across the country”.

Water companies have a legal deadline of 2025 to publish real-time data on sewage discharges, but Dr Lipp said it should be provided sooner since companies already monitor this information internally.

Southern Water and South West Water are currently the only other water companies who provide limited real-time information on sewage discharges, related to beaches only.

On Thursday i reported that nearly 100 beaches along England’s south coast had likely been impacted by a deluge of sewage.

The recent discharges have raised questions around how Britain’s sewage network will be able to cope with climate change, which is already bringing more intense rainfall to the UK.

A Thames Water spokesperson said: “We are working hard to make these discharges unnecessary and have published plans to upgrade over 250 of our sewage treatment works and sewers to treat the high volumes of incoming sewage and reduce the need for overflows during wet weather.

“Taking action to improve the health of rivers is a key focus for us and we want to lead the way with our transparent approach to data. We remain the only company to provide live alerts for all untreated discharges and this ‘near real-time’ data is available to customers as a map on our website and is also available through an open data platform for third parties, such as swimming and environmental groups to use.”