Water engineers will be visiting homes in Collier Row over the next few weeks to apply fluorescent dye in sinks, dishwashers and toilets.

The “track and trace” dye method is to find misconnected pipes and find sewage that ends up in the wrong place.

It is part of a Thames Water investigation which began this month and will run into 2021.

If pipes from toilets, washing machines and dishwashers are not connected properly it risks wastewater - water contaminated with chemicals from household appliances - getting into the wrong sewer system and damaging the environment.

Thames Water says it has uncovered 8,000 incorrectly plumbed toilets, washing machines and dishwashers over the past five years across London and the Thames valley that pollute rivers.

The dye is harmless and disappears once it gets into larger bodies of water, posing no risk to water quality or wildlife.

Misconnections most commonly occur during new builds and property renovations, when appliances are connected to the wrong sewer by developers or builders.

The company’s waste networks team is now planning to carry out more than 1,000 additional inspections across the region, with a focus on the capital, to ensure misconnections are avoided.

Stephen Barry, Thames Water’s environmental protection manager, said: “Household appliances which are connected to the wrong drainage pipe can have a serious impact on the environment.

“Most misconnections have been done entirely by accident but we would urge anyone installing a new appliance or fitting new connections to make sure they’re plumbed in properly. Failing to do so can also lead to extremely expensive repair bills.

“We’re pleased to have found so many of these misconnections over the past five years and helped owners fix them but we’re determined to keep doing more to ensure all wastewater is taken to our sewage works where it can be safely treated.”

The most commonly-found misconnection was on kitchen sinks, followed by washing machines and hand basins. Other appliances included dishwashers, toilets, baths and showers.

Responsibility for fixing misconnections lies with the property owner.