The misconnected pipes polluting urban rivers

Hidden plumbing errors are sending untreated household sewage into rivers, polluting waterways without residents' knowledge. One south-west London river has been badly affected by these misconnections.

A misconnection happens when wastewater is incorrectly diverted into surface drains, leading to pollution in nearby waterways.

Pollutants may include raw sewage, chemicals and physical debris which are harmful to wildlife and lead to further degradation of river ecosystems, according to Dr Isobel Ollard from the South East Rivers Trust (SERT).

The Wandle, a 12-mile (19km) chalk stream running from Carshalton to the Thames at Wandsworth, is one place where these contaminants are being found.

Ollard said misconnections like these bypass the treatment normally carried out at sewage treatment works.

An example of this kind of pollution was recently found at Watermeads Nature Reserve (which connects to the Wandle) where a cloudy, milky-looking water was seen trickling from a concrete outlet into the river.

Containment booms installed by Thames Water caught some of the discharge, preventing some of the substance from spreading further downstream, but the water remains contaminated.

Ollard explained the pale colour of the discharge indicated it was likely coming from a washing machine in a nearby property that has been incorrectly connected to the water network, allowing wastewater and detergents to enter the river.

Chalk rivers like the Wandle are rare and fragile ecosystems supporting diverse wildlife, with only around 200 worldwide, making them particularly vulnerable to pollution.

According to Ollard, misconnections are particularly difficult to deal with because identifying the source of the problem - and who is responsible - is often complex.

Thames Water is responsible for investigating leaks and tracing them through drainage networks.

However, once a misconnection is identified and traced to a property, it is a legal requirement for the homeowner to fix it.

The company said it has investigated more than 20 suspected misconnections in the past three years.

Ollard said many homeowners are unaware their property is misconnected, and that older homes can have historic plumbing errors that only come to light once pollution is detected in a river.

These issues are also not usually identified in surveys, meaning people may buy a home without realising it has an issue.

She said: "Then they will get a letter saying it has been identified and they will then be required to do the work, which costs thousands of pounds."

Leonie Cooper, Labour London assembly member for Merton and Wandsworth and deputy chair of the environment committee urged residents to ensure drainage systems are correctly installed when carrying out work or buying property.

Last year, Thames Water said it had identified 2,294 plumbing misconnections across London over the previous five years.

Ollard encouraged residents to reconnect with their local rivers, saying this would help bring greater awareness to the issue.

She said: "In turn, the more we notice and care about our rivers, the better we are able to care for and protect them."

A Thames Water spokesperson said: "We actively investigate suspected misconnections and support local projects to raise awareness and involve communities in protecting their environment.

"All pollution reports are investigated within two hours. Where third-party issues are identified, we work with property owners or local authorities to resolve them, with more complex cases addressed through our Surface Water Outfall Programme."