Many homes have two separate drainage systems: one for foul water from toilets, sinks, baths and appliances, which goes to a sewage treatment works, and one for rainwater, which often goes straight to a local stream, river or the sea.
A misconnection is when foul water ends up in the rainwater system. The waste then flows untreated into the environment.
How misconnections happen
- A washing machine or dishwasher plumbed into the nearest pipe, which turns out to be a rainwater downpipe or surface water gully.
- Extensions and kitchen moves, where new sinks or toilets are connected to the wrong drain.
- Garage and outbuilding conversions with new toilets or utility rooms.
- DIY plumbing, where it is not obvious which drain is which.
Many homeowners have no idea their property is misconnected, especially if the work was done before they moved in.
Why it matters
- Pollution: detergents, food waste and sewage harm wildlife in streams, rivers and coastal waters.
- Your responsibility: the owner of the property is usually responsible for putting a misconnection right. The water company or environmental regulators can require it to be fixed.
- Buying and selling: misconnections can come up during building work or a survey, and are better found and fixed on your terms.
Signs your home may be misconnected
- Soapy or grey water, food debris or smells in a gully that should only take rainwater
- A washing machine or sink waste pipe running into a rainwater downpipe
- Extensions or utility rooms added without building control sign-off
- A local stream or surface water outfall with foam or smells, traced back to your street
How to check
Start by identifying which drains are which. Rainwater downpipes and gullies that take only roof water should go to the surface water system; anything from inside the house should go to the foul system. The national ConnectRight campaign, supported by water companies, has guidance and diagrams to help homeowners check.
A CCTV drain survey, or a dye test where coloured dye is run through a fitting to see where it appears, shows exactly where each pipe goes.
Fixing it
Usually the wrongly connected pipe needs to be rerouted to the foul drain. Depending on the layout, that can be a simple change to a waste pipe or a larger job involving new underground pipework. We can explain the options after a survey. See drain repairs.
Areas with combined sewers
In some older areas, a single combined sewer takes both rainwater and foul water, so misconnections in the same sense do not arise. Your water company can tell you which system serves your street. See also how to find your drains and inspection chambers.