Sewer blockages and flooding

Article by Emma Lofthouse 17 May 2018

The amount of water entering our drains and sewers is ever increasing due to wetter climates and the increased use of hard surfacing in developments causing more surface water runoff. Add in the thousands of blockages occurring in our sewers every year and this can result in an increase in easily avoidable flood events. By following simple actions, everyone can help to reduce the number of sewer blockages and in turn lessen the chance of flooding.


Why sewers block

Every year in the North West alone there are 28,000 avoidable sewer blockages. The main causes of these are due to the incorrect flushing of unsuitable objects down the toilet, such as wet wipes and cotton buds, and the disposal of oils and fats down the kitchen sink.

The build up of these items, especially cooking fats and wet wipes, results in a rock-hard, growing blockage, sometimes known as a ‘fatberg’, that will eventually fully restrict the flow of sewage water through the pipes. Consequently, sewage water can back up and be forced up through toilets and sinks in households, into your garden, or could burst up through manhole covers and flood roads and public areas. This can be dangerous due to harmful microbes that may be present in the water, and the difficulty of cleaning it up afterwards.


Cooking Oil


One study found that wet wipes made up around 93% of the material causing sewer blockages, showing that these are a big problem, especially when some wipes labelled as ‘flushable’ have actually been found not to break down.

A recent Channel 4 documentary, ‘Fatberg Autopsy: Secrets of the Sewers’, investigated 5 tonnes of a fatberg in London estimated to be at least 750m long. You can also visit a fatberg exhibition at the Museum of London.



Property owners are responsible for the maintenance and repair of  ‘private drains’, which are those that take waste water away from only their property, up to the point where it connects to a pipe from another property. If a blockage occurs in a private drain, the property owner is responsible for it.

Water companies are responsible for maintenance and repairs of public sewers, and drains that lie outside the boundary of a property and connect to public sewers. If a blockage happens in these drains, your water company is responsible for it.

To find out more about responsibilities for general flooding, see our ‘Who is responsible for managing flood risk?’ resource here.




What is being done?

Water companies across the UK have launched campaigns to raise awareness of sewer blockages and encourage people to think more carefully about what they are putting down their drains.

Visit your local water company's website to see how you can help prevent blockages and sewage water floods in your area.


How you can help

The most helpful thing you can do is remember to only flush the three P’s down your toilet: pee, poo and toilet paper.

Other top tips:

  • Place a bin in your bathroom for items such as wet wipes and cotton buds.
  • Collect leftover cooking fats and oils in a heat resistant pot, or ‘fat trap’, and dispose of with your household waste.
  • Wipe up small amounts of grease and leftovers from pans or plates with kitchen roll and bin before washing up.
  • Use a sink strainer to capture food scraps and dispose with your household waste.
  • Wrap coffee grounds in newspaper and place them in the bin.

As well as looking after our drainage systems, we can also increase the use of Sustainable Drainage Systems (SuDS) in both existing properties and future developments to manage and reduce the volume of water entering sewers, and instead channel the water into temporary storage or the surrounding land.


Sources: The Guardian, United Utilities, Thames Water, Severn Trent


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