Top of main content

Sewer flooding causes

What causes sewer flooding? Identifying the issue makes it easier to know who's responsible for fixing it.

The three main causes of sewer flooding are:

Watch our video to see why sewer flooding happens.

Heavy or continued rainfall

When it rains heavily, or for a long time, the extra water can overwhelm our sewers. The sewer fills, backs-up pipes and drains and can flood properties, roads and streets with sewage. During heavy rain, storm overflow discharges are more frequent too. With climate change causing more intense rainfall, this is becoming a bigger issue. 

We're responsible for maintaining our sewer network and have a long-term plan for preventing sewer flooding. We're working towards reducing storm overflow usage to improve river health.

Continued heavy rain also causes river, groundwater and surface water flooding. Some of our sewers date back to Victorian times. They don't have the capacity to carry flood water and were designed for a much lower population.

Local authorities and the Environment Agency (EA) are responsible for groundwater, river and surface water flooding. We'll be working with them to manage flood water entering the sewer system. View our list of emergency contacts for flooding.

River flooding

Heavy rainfall can cause rivers to swell and burst their banks. River water floods the surrounding land and buildings, ending up back in our sewers. 

Groundwater flooding

Groundwater flooding seeps into our sewer system. Some areas are more likely to get groundwater flooding, for example, river valleys. 

This type of flooding happens slowly. It can last for months after heavy or continued rainfall. 

Surface water flooding

A lot of our green areas are being paved over and built on. This means we have a lot less natural drainage, as rain can't absorb into the soil. The surface water ends up in our sewers instead. If you're building an extension or new driveway, think about rainwater drainage.   

Damage and system failure

It's our responsibility to maintain and repair the public sewer system. Burst pipes, sewer collapse or pumping station failure can all cause sewer flooding. If you see a blockage or flooding when you're out and about, you can report a problem to us here. 

We’re working round the clock to respond to sewer flooding incidents. We're also investing in our network, increasing sewer capacity and reducing the need for storm overflows.