As it flows through East Barnet, Pymmes Brook occasionally gives north London a bucolic feel. At points, this tributary of the Lea river winds its way through patches of parkland and forest. At one pleasant and grassy spot, a large willow stoops over the water.
There is, however, something nasty lurking under the surface: because houses in the neighbourhood have not had their toilets connected to the sewage system properly, Pymmes Brook has effectively become an open sewer.
Under the willow, an outlet flows into the tributary. This pipe is only supposed to carry rainwater that flows off roads and gutters. Because toilets flush into this “surface water” system, the outlet frequently releases very high levels of faecal bacteria. These bugs, which should have been dealt with at a sewage treatment works, can cause illness.
The problem, which is likely to affect hundreds of other urban streams, reflects a lack of diligence over how homes get rid of their sewage. Much of outer London, in common with other cities around the UK, is served by two drainage networks. One set of pipes should take “foul waste”, which includes what goes into the toilet, to sewage treatment works.
Another set of pipes should send surface water — rainfall run-off — to the nearest river. When appliances and bathrooms are “misconnected” into surface water drains, the wastewater and raw sewage ends up in rivers. This contributes to elevated phosphate and ammonia levels, which degrade river ecosystems. Misconnections have been cited by the Environment Agency as a reason for water bodies across London not achieving “good” ecological status.
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Dr Veronica Edmonds-Brown of the University of Hertfordshire has spent decades monitoring water quality. Her work gives a glimpse of the scale of the problem. Beneath the willow tree in East Barnet, faecal bacteria levels — an indicator of human waste — are routinely about 6,000 colony-forming units (CFUs) per 100ml of water.
Elsewhere along the Lea, she has recorded levels at surface water outlets as high as 5 million CFUs. It is difficult to make a direct comparison, because different microbes are picked up depending on who is testing. For reference, however, the maximum level of E. coli bacteria allowed by the Environment Agency at a bathing beach is just 500 CFUs per 100ml.
There are anecdotal reports of pets becoming ill. “Local vets complain that dogs have gastrointestinal problems after playing in the brook,” said Edmonds-Brown. “And if the kids are playing and their football goes in, they’ll go in, too.”
The issue is likely to be widespread across urban areas. In 2020, Edmonds-Brown tested 45 surface water outlets feeding into the Lea River. All but one had levels of bacteria that indicated contamination from human waste. At some, there were found solid pieces of fecal matter.
In 2016-17, volunteers for the Zoological Society of London looked at 1,177 surface water outfalls across Greater London. Its monitoring was less thorough than Edmonds-Brown’s, because it relied on volunteers looking for visible signs of pollution.
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Its survey still found 356 surface water outfalls that showed clear signs of contamination — including discoloured water, sewage fungus, bad smells and sanitary products.
About one in 20 outlets had “a pollution problem requiring urgent attention … This represents a substantial pollution issue that is degrading the health of rivers in the capital,” the Zoological Society concluded.
What could be done about it? Edmonds-Brown believes that when houses are sold, sellers should be obliged to have drains checked and to make sure toilets and appliances like washing machines are correctly plumbed in. She also wants better monitoring of extensions and new-build houses, to make sure builders and developers aren’t linking bathrooms to surface water pipes.
She concedes, though, that this would be expensive. Her first priority is to highlight the issue. “A lot of people would want to put this right, they just don’t know about it,” she said. “It’s a very well hidden form of pollution.”
