Faulty drains threaten Thames water quality

Raw sewage and other pollutants are being inadvertently dumped into the Thames by homes and business across London due to misconnected plumbing, according to the most comprehensive survey of London’s rivers undertaken in recent years, led by international conservation charity ZSL (Zoological Society of London). 

Faulty drains threaten Thames water quality

The study, conducted in collaboration with partners including the Environment Agency, Thames Water, Thames21, Catchment Partnerships in London (CPiL) and over 100 trained volunteers, assessed 1,177 outfalls (drains that send surface water into rivers).  Signs of contamination including sewage fungus were found in 356 of these locations, along with definite pollution problems in 269 cases – equating to an average of 2-3 polluting outfalls for every kilometre of river surveyed. 

The resulting data indicates that a large number of properties across London are sending foul waste from toilets, sinks and washing machines into rivers via the surface water drainage system, rather than to sewage treatment works. This pollution is degrading the ecological health of rivers, restricting the amount of wildlife they can support.  

Joe Pecorelli, project manager for ZSL’s Estuaries and Freshwater team, said: “Based on our comprehensive ‘citizen science’ survey of London’s surface water outfalls, we hope the sobering findings of this report will encourage positive change for the Capital’s waterways. Alongside our partners, we’re calling for significant increase in investment to address misconnections in household and commercial plumbing systems across London. 

“Approximately 600km of rivers and streams flow through Greater London into the Tidal Thames. Together, these waterways represent an invaluable habitat for wildlife, from eels and water voles, to kingfishers and dragonflies – but a history of poor water quality, badly-designed flood defences and adaptations for navigation have prevented many of them from achieving their full ecological potential. As a result, just one of the 39 rivers in Greater London has so far qualified as having ‘good’ ecological status or potential, under the Water Framework Directive legislation designed to protect and improve the UK’s aquatic environments. ”

“We’re calling on home and businesses owners across the Capital to have their plumbing checked for misconnections. We’re also asking local authorities to ensure the plumbing systems of new developments meet correct standards, and that funding is increased for industry-wide awareness schemes like ConnectRight. Working together, we can make a real difference to water quality and wildlife across the Thames region by tackling this longstanding issue”. 

The data for this report was collected via an innovative, citizen science-based approach dubbed ‘Outfall Safari’, whereby teams of volunteers were able to survey river banks and use a specially-created app to geotag, photograph and assess outfalls for evidence of pollution. This invaluable data was then sent back for analysis by ZSL, and reporting to the Environment Agency and Thames Water.

Debbie Leach, Chief Executive of Thames21, London’s leading dedicated waterways charity, said: "There is a massive environmental accident happening across London, and it is devastating our rivers. But because it is happening day after day, it isn't making the news. That has to change. Each day, more and more waste water pipes from our houses are being connected up to rainwater drains going straight into rivers, and the result is horrendous. Therefore we were delighted to use our long-established skills, of motivating and training volunteers who care for their stretch of river, to contribute to this fantastic work.”

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