Sewer flooding

Sewer flooding

Sewer flooding is a very serious issue and we are committed to reducing the risk of it occurring in our region.

Whilst we are able to identify the cause and resolve a great number of flooding problems quickly, there are occasions when more detailed investigations are needed.

To ensure that all customers receive the same high level of service, all incidents of sewer flooding are dealt with under our sewer flooding procedures.

Local authority map

Local authorities function as landlords for council owned houses and are responsible for maintaining the drains for these properties. They are also responsible for maintaining some highway drains. Please see the adjacent picture which is an example of a highway drain. This interactive map shows all of the local authorities in our region and includes direct links to their websites.

If you are experiencing flooding which you believe has occurred from the highway, you can use the map to contact your local authority about the flooding.

Sewer Flooding causes and liability explained

Northumberland Northumberland Northumberland Newcastle Gateshead North Tyneside South Shields Sunderland Durham Hartlepool Darlington Stockton-on-Tees Redcar and Cleveland Middlesbrough  Cumbria County Council  North Yorkshire County Council
Sewer flooding causes

Sewer flooding is a distressing experience for our customers and there are a number of reasons why sewer flooding occurs:

Third party interference

The public sewerage system is an open network and can therefore be subject to third party interference causing blockages. Flooding due to blockages can occur from the incorrect disposal of items such as wet wipes, sanitary products, fats, oils and grease. Intrusion of tree roots into the sewerage network can also cause blockages which can lead to flooding. Damage to the sewerage network caused by other utility companies/construction activity can cause structural damage to the pipes resulting in blockages and flooding also.

Exceptional weather

The sewerage network is built to accommodate a normal level of flow based on factors such as the size of the drainage area, the number of customers and predicted volumes of rainfall. During more intense rainfall events, the sewers may not be able to cope with volumes that exceed the predicted rainfall volumes.

Incapacity in the network

Sewers were originally built for the communities they served. However, due to population growth and developers’ automatic right of connection to the sewerage network, flows in some communities have increased which in some cases may lead to incapacity in the sewerage network. Therefore, some parts of the network may not be able to cope with flows during moderate rainfall incidents.

Investing in the sewerage network

If flooding has been caused due to incapacity in the Northumbrian Water network we will assess the financial cost of resolving this issue. We prioritise investment to ensure that we comply with financial controls imposed by our regulator, OFWAT. We regularly assess if investment in the sewerage network meets the criteria set by OFWAT. When criteria for investment are satisfied we will invest in the sewerage network to increase the capacity and reduce the risk of future flooding. When criteria for investment are not met, we will carry out property flooding protection if appropriate and continue to reassess regularly against the criteria.

Storm return periods

To help understand if flooding was caused by incapacity in the network or exceptional weather, we assess rainfall incidents based on ‘storm return periods’. The storm return period is defined as the average period of time expected to elapse between occurrences of rainfall incidents at a certain place.

A 1 in 20 year storm return period refers to a storm which has a 5% chance of being equalled or exceeded in any given year and can occur at any point in that year. You can also get multiple storms of the same return period in one year. This classification is based on analysis of historical rainfall data by the National Environmental Research Council.

Urban creep

Urban creep is another factor in causing our public sewerage network to potentially overflow. Urban creep occurs when once permeable areas such as grass are changed to impermeable areas such as concrete within the urban environment. Typical examples are the construction of patios, parking, house extensions, etc which then cause water to run over the land, rather than seep into the previously permeable area, and into our public sewers.


Around 300,000 UK homes are sending wastewater from washing machines, sinks, baths and even the toilet direct to their local river instead of to the sewage treatment works. This is caused when mistakes are made in the way that waste pipes are connected around our homes.

The pollution resulting from misconnections can have a dramatic impact on rivers. It can bring visual and odour nuisance and cause health risk due to the levels of untreated sewage. This pollution impacts on the ecology of our streams and rivers, affects their use and can bring failures in bathing water standards.

Homeowners are responsible by law for making sure their waste pipes are properly connected – even if they did not carry out the plumbing that caused the misconnection. In rented properties, the landlord is responsible. Fixing the problems is often straightforward and not too costly.

Sometimes the domestic surface water pipes (roofs and gutters) are wrongly connected to the foul sewer. When it rains, the foul sewer may become overloaded with the rainwater and cause flooding.

Homeowners are also responsible for ensuring their private surface water drainage is properly connected.

Summary of responsibilities for flooding

Flooding Sources and Mechanisms Northumbrian Water Local Authority Environment Agency Riparian Owners*
Surface Water
Runoff as a result of high intensity rainfall when water is ponding or flowing over the ground surface before it enters the underground drainage network or a watercourse.
Flooding from Ordinary Watercourse i.e. watercourse that does not connect to a main river
Flooding that occurs as a result of an ordinary watercourse overflowing.
Flooding that occurs when the ground is waterlogged and water rises to the surface.
Main Rivers
Flooding that occurs when a main river cannot cope with the volume of water draining into it and the river overflows.
This occurs when a high tide or storm overflows on to coastal land or coastal flood defences.
This occurs when a reservoir/canal embankment or control fails and releases a large amount of water into the downstream area.
Public Sewer
Flooding that occurs when the capacity of the underground drainage system is exceeded, resulting in flooding inside and outside of buildings.
Burst Water Pipes/Mains
Flooding that occurs when a water pipe/main bursts.
Highway Flooding
This is when surface water flooding occurs on a highway.

* Riparian owners are those who own land adjoining a watercourse. They are presumed to own the land up to the centre of the watercourse, unless it is owned by someone else.

Liability for flooding

Under the Water Industry Act 1991, sewerage companies are generally not liable for flooding from public sewers. OFWAT accepts this exemption because without it, sewerage companies would face large liabilities for sewer flooding which would lead to substantial increases in customers’ bills. For a sewerage company to be held liable, it has to be proven that it has been negligent i.e. we have done something, or failed to do something, which resulted in the flooding.

Recognising the impact of flooding

We do recognise that flooding incidents cause distress and inconvenience, therefore we may make you a payment the equivalent to a portion of your annual sewerage charges when the flooding has originated from our sewerage network.

Impact of internal flooding

If the inside of your property is flooded from one of our sewers, we will pay you an amount equal to your full sewerage charge for the year or £150, whichever is more (up to a maximum of £1000) in line with our guaranteed standards of service.

From 1 April 2015, if your property is placed on the internal flooding register, we will suspend your annual sewerage charges until your property is removed from the register. The suspension will be from the date that your property was placed on the register. You will still continue to receive a payment in line with our guaranteed standards of service should you suffer any further flooding whilst your property is on the register.

Impact of external flooding

If the outside of your property within your boundary is flooded, you may be eligible for a payment equal to 50% of your sewerage charge for the year or £75, whichever is more (up to a maximum of £500) in line with our guaranteed standards of service. To be eligible for a payment for external flooding, certain criteria must be met in relation to the size of the external area affected by flooding and the impact the flooding has had on your use of this external area e.g. blocked access.

In order to be eligible for a payment, you must notify us of the flooding within 3 months of the incident.

If you are entitled to these payments and we do not make the payment within 20 working days of being notified of the flooding event, we will pay you an additional £20, (£50 for a business customer).

We are unable to make a payment in the following circumstances:

• If the flooding is caused by you.
• If the flooding is caused by exceptional rainfall events.
• If our investigations confirm that the flooding was as a result of issues not related to Northumbrian Water’s sewerage network e.g. surface water running over land, river inundation or highway drainage.

Downloadable content

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    Our promise to you

    This leaflet details the standards of service we guarantee to provide to you.


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    Further investigations

    Into your sewer flooding.


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    What to do

    If you experience sewer flooding.


Call 0800 328 7648

for the freephone floodline.

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