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Plumbing Misconnections

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

The problem is caused by wrongly connected pipework from homes and businesses that discharge to the surface water sewer, instead of the foul water sewer. This results in raw sewage, chemicals and detergents being diverted into the surface drainage system and potentially into bathing waters.

Half of UK homes are on separate sewers, 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, suggests around 140,000 properties, but in some areas investigations have found up to 1 in 5 properties misconnected. The real UK total could be more than 300,000.

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

How does this occur?

Waste water 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 in some places.

Most houses built after the 1920s had separate surface and foul water drains, so that the sewage could be sent directly to the sewage treatment works and the surface water disposed of locally via a watercourse or similar. This did solve one problem, as it relieved pressure on overloaded combined sewer pipes – unfortunately, it caused another problem. Individuals who are not aware of the big picture tend to misconnect their washing machine/dishwasher/sink to the rainwater pipe, or discharge into the same rainwater gully. This results in pollution of their local watercourse or bathing water.   

Property conversions, the DIY culture, ignorance of sewers amongst the public and building trade all add to the problem. The most common misconnections are washing machines (35%), sinks (10-15%), dishwashers (10-15%), toilets (5%), whole houses (5%).

This link to the Thames Water website shows a video that helps to show the impact of misconnections –

Misconnections to a sewer can result in a fine of thousands of pounds, but the cumulative impact is very significant in many urban areas of Britain.

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.

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?

  • Is your property built after 1920? (In some areas even before the 1920s – think typical box four semi-detached properties.)
  • 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?

If the answer to any one of these questions is yes, visit the ConnectRight website – – you’ll find lots of information and diagrams to help you to ascertain if there is a misconnection on your property.

The CIPHE has also put together a drainage survey, which will test your knowledge on the plumbing system in your property.

If you believe there is a problem and need a professional plumber, you can visit the Find a Plumber section on this website. Alternatively visit