Our challenges

We don't usually like to think too much about what happens when we flush the loo but storm overflows are an important part of the sewerage network which takes away the used water from our homes.

We call them storm overflows and, while they probably don't crop up in your everyday conversation, they play a major part in preventing flooding in our streets and homes. They act as a pressure relief valve when there is too much rainfall, allowing rain water, mixed with sewage, to rise inside the sewer and eventually enter a separate pipe which flows into a river or the sea.

How these overflows work

• When the sewer system is operating normally, sewage leaves our homes and businesses, sometimes mixed with rainwater, and is sent to one of our nearest treatment works. Sewers are typically only 15% full when it is dry
• If an area is hit by really heavy rain, like the kind we have seen in more recent summers, the sewers sometimes become completely full of water and the sewage starts backing up
• If there was no storm overflow in place, this sewage could enter homes and streets, as the wastewater would force its way out of the network of pipes to the surface, often rising up through manhole covers.
• With a storm overflow in place, the rain water, mixed with sewage, will rise inside the sewer and eventually enter a separate pipe which runs off the main sewer and flows into a river or the sea
• Under strict conditions, and with the permission of the Environment Agency, water companies like United Utilities are allowed to spill wastewater into the river and sea because it is accepted there is a finite capacity inside sewer pipes
• Even if a sewer is completely unobstructed and of the approved size, there could still be times when storm waters completely fill them
• After heavy rainfall, groundwater can find its way into combined sewers, adding to the amount of water in the pipe and increasing the chance that a spill may occur. 

The Environment Agency estimates these storm overflows lead to around 30 per cent of sea pollution in the North West, with water quality along our coastline also affected by lots of other factors.

Customer and stakeholder feedback is clear – the outcome they want to see is improving sea and river water quality and we agree. River water quality is measured by whether it is achieving good ecological status under the Water Framework Directive. Where rivers are failing to meet this status, the reasons, known as RNAGs or “reasons for not achieving good ecological status”, are assigned to organisations with a responsibility to act to improve water quality.

In 2019 United Utilities was allocated 512 RNAGs, representing 10.5% of the total in the North West. As a result of our investment in wastewater treatment and storm overflow operation we forecast we will have reduced RNAGs by over 75% by 2025, leaving with us 118 RNAGs to address. With our proposed investment plan to 2030, this will further reduce the number of RNAGs to 80, 2.2% of the total.

What this means is that the remaining issues to be tackled to ensure North West rivers meet good ecological status will sit predominately with other organisations. We will continue to work closely in partnership with those organisations as, quite often, the actions they can take will also benefit us, for example improving how surface water is managed to reduce the risk of flooding.

We are committed to improving our rivers and beaches and working with our partners on tackling these issues, such as rain running off highways and farm land, private drainage being incorrectly connected and people not cleaning up after their dogs.

Additional challenges

In addition to our specific challenges with CSOs, there are also a number of wider issues impacting water quality across the North West.