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Sewer blockages and flooding

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 flood events that could be easily avoidable. 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 around 28,000 avoidable sewer blockages, costing United Utilities £10million to clear. The main causes of these are due to the incorrect flushing of unsuitable objects such as wet wipes and cotton buds down the toilet, and the disposal of fats, oils and greases (FOGs) 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 can eventually fully restrict the flow of sewage water through the pipes. Consequently, sewage water can back up and be forced back 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.

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.

In 2019, United Utilities discovered the North West’s biggest fatberg in Liverpool, stretching 250 metres long and weighing a massive 400 tonnes! It consisted of fats, oils, wet wipes and other items that definitely don’t belong in our sewers. United Utilities then have the challenge of removing the fatberg to help water flow more freely in the sewer, which can take around 6 weeks. Watch how the fatberg is being tackled here.



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 repair of public sewers and the 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 flood water?’ 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.


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, cotton buds and sanitary products.
    • Collect leftover cooking fats and oils in a heat resistant pot, or ‘fat trap’, and dispose with your household waste.
    • Before washing up, wipe up small amounts of grease and leftovers from pans and crumbs on plates with kitchen roll and bin it!
    • 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.

Take a look at this fun idea below from the Unlocktober campaign 2019 of making your own bird feed fat balls with leftover fats!


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.


Download our resource on The Flood Hub for more info here.


Sources: United Utilities, Thames Water, The Guardian, The Rivers Trust, Severn Trent, Unblocktober

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