Misplumbed homes are sending sewage into four London rivers, survey finds

Household plumbing faults are sending human waste into four of London’s smaller rivers, according to the latest volunteer survey run by the Zoological Society of London (ZSL). The Brent had the most polluting pipes. Volunteers also found problems on the Wandle and the Ravensbourne in south London, and on the Pinn in west London.

For the past decade, ZSL’s Outfall Safari programme has trained volunteers to walk riverbanks and spot drainage pipes that carry sewage from homes into the water. The cause is misconnections, where wastewater ends up in a watercourse instead of the sewer. A single appliance in one home can be to blame, often after renovations or home improvements, but whole blocks of flats or entire estates can be affected too.

River Brent pollution the worst in the survey

Volunteers covered 22.4km of the Brent and inspected 123 outfalls, finding 44 that were polluting. Emergency alerts went to Thames Water for 15 high-priority incidents. “The Brent is a hotspot for poor water quality,” said Ella Carbery-Tarrant, the ZSL project officer leading the programme, who called some of the watercourses “pretty disgusting”.

Last month City Hall appointed a full-time enforcement officer to deal with misconnections across west London, after repeated pollution in the Brent.

Polluting outfalls on the other rivers

The Wandle came out better. Of 105 outfalls volunteers checked there, 90 had no visible signs of pollution, while nine were actively polluting. Two of the nine were bad enough for Thames Water and the Environment Agency to be alerted straight away. Ms Carbery-Tarrant said the river was not too bad compared with other catchments, though misconnections are a long-running issue there.

On the Ravensbourne, volunteers found 18 polluting outfalls, six of which needed emergency alerts. The Pinn had 17, with three severe cases passed to Thames Water.

Thames Water also hunts for misconnections through its own Surface Water Outfall Programme, which relies on dye testing and surveys of homes. Its recent work on the Wandle, a 12-mile chalk stream that flows from Carshalton to the Thames at Wandsworth, found that eight properties on Wandle Road had 77 appliances between them connected to rainwater pipes by mistake.

In north London, the citizen group Haringey Water Squad keeps a regular watch on the River Moselle, which runs largely out of sight through the area. Its volunteers said their checks where the brook passes through Lordship Recreation Ground in Tottenham turned up sanitary waste, and chemical levels there were high.