Plumbing misconnections



It’s hard to believe, but it’s likely that hundreds of thousands of UK properties have misconnections in the plumbing system causing pollution to streams, rivers and on local beaches.

The problem is caused by erroneously connected pipework from homes and businesses that discharge to the surface water sewer, instead of the foul water sewer. Misconnected pipes allow nasty wastewater and chemicals to drain away into rivers and streams, damaging the environment and harming wildlife. All household goods should be plumbed into the wastewater sewer, so the water can be taken away and treated.

Half of UK homes are on separate sewers, and although the exact number with misconnections is difficult to estimate due to the complexity of the housing stock, the UK Water Industry report, published in 2013, suggested there were around 140,000 properties that were misconnected. However, in some areas, local investigations have found up to 1 in 5 properties misconnected and the actual total could be over 300,000 homes.

This is a very common problem that is not understood by many, including homeowners, DIYers and property developers, some of whom can be taken to court over misconnections to a sewer, if it results in more serious pollution.

How does this occur?

Wastewater from inside our homes, e.g. water from WCs, bidets, kitchen sinks and bathroom washbasins, showers, washing machines and dishwashers, should all be piped underground to the local sewage treatment works, where it is treated before discharge to a river or stream. The above-ground pipework is referred to as sanitary pipework; the underground pipework is referred to as foul drains and foul sewers.

Rainwater that falls onto our roofs, patios and drives should be directed to a surface water drain or a soakaway. The above-ground system of gutters and rainwater pipes is referred to as roof drainage; the underground pipework is referred to as surface water drains and surface water sewers.

Generally, houses built before the 1920s and many even after that in some areas, had a combined sewer so all drainage, whether clean or foul, went into the same pipe. This meant that in times of heavy rains, the sewer would overflow and discharge diluted sewage into rivers and overflows. Such combined sewer overflows still cause problems today.

Most houses built after the 1920s had separate surface and foul water drains, meaning sewage could be sent directly to the sewage treatment works and the surface water disposed of locally via a watercourse or similar. Although this did solve one problem, as it relieved pressure on overloaded combined sewer pipes, unfortunately it caused another as it has led to misconnections of washing machines/dishwashers/sinks to the rainwater pipe or to discharge into the same rainwater gully, resulting in pollution of the local watercourse or bathing water.

Property conversions, the DIY culture, ignorance of sewers amongst the public and building trade have all added to the problem.

There are lots of nasty pollutants in sewerage that present environmental and health risks in water bodies, including some persistent chemicals we use every day in our homes. Almost all urban streams are affected to some extent.

Don't get caught out by plumbing misconnections

  • Up to 1-in-5 properties misconnected in some areas
  • DEFRA estimate between 150,000 and 500,000 properties with a drain misconnection
  • Homeowners with misconnections that cause significant damage are liable for £50,000 fine or up to 12-months imprisonment
  • It is the property owner’s responsibility to resolve misconnections on their homes
  • The most common misconnections are washing machines (35%), dishwashers (15%) sinks (10-15%), and toilets (5%).

Who is responsible?

The property owner must fix any misconnections, although water companies generally are responsible for below ground shared drainage.

How can I tell if I have a sewer misconnection?

  • Was your property built after 1920?
  • Do you have more than one manhole inspection cover?
  • Do any other pipes, other than rainwater pipes connect to, or discharge into the same gully as a rainwater pipe?
  • Have there been any extensions, alterations or new bathrooms/ kitchens installed?

The more yeses to the above questions, the greater the likelihood that there has been a plumbing misconnection at your property.

You can find out more on the ConnectRight website.

CIPHE Drainage Survey

Check your knowledge of the plumbing system at your home with our survey.



You’ll find information and diagrams to help ascertain if there is a misconnection on your property.

Find out more

Find a plumber or heating engineer

If you believe there is a problem and need a professional plumber, find a qualified professional member of the CIPHE.

Find a Plumber