Southern Water marks progress in its storm overflow reduction plan
Our £1.5bn Clean Rivers and Seas Plan has prevented more than 700 storm overflow releases in its first year
Reducing storm overflows across our region
We have delivered early, measurable progress in our £1.5bn Clean Rivers and Seas Plan, preventing hundreds of storm overflow releases in the last 12 months.
With public concern about storm overflows at an all‑time high, we’re accelerating action across the South. More than £70m has already been invested in sustainable solutions, infrastructure upgrades and cutting‑edge AI, with interventions now deployed at 95 of the most environmentally sensitive overflows, including 29 projects brought forward ahead of schedule.
These early results show the plan beginning to make a difference, even as the scale of the challenge remains significant. Storm overflows remain a major issue nationally, and Southern Water acknowledges that sustained, long‑term action is needed to deliver the step‑change customers and communities expect.
What causes storm overflows?
A key part of tackling storm overflows is understanding why they happen. In many areas, rainwater from roofs, roads and hard surfaces still flow into the same pipes that carry wastewater. In others, particularly in chalk landscapes, rising groundwater enters the sewer system during wet months. When these flows overwhelm the network, storm overflows act as a safety valve to prevent flooding in homes, schools and streets.
This doesn’t make storm overflows acceptable, but it does show that the root challenge is managing and stopping rainwater and groundwater entering our sewers. Without addressing this, we cannot reduce storm overflows in a lasting way.
Early improvements already making a difference. Examples include:
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Hampshire – we’ve completed over 200 roof separations in Fareham and Gosport - taking rain run off out of sewers and into surface water drainage systems, with a further 44 properties currently in progress in Emsworth
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Isle of Wight – Intricate pipework upgrades and the installation of AI smart sewer gates have already prevented 57 storm overflow releases.
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Kent – Reconfigured our Swalecliffe site which has reduced storm overflows by 36%, and added two smart sewer gates in Whitstable, which react to incoming rainfall and create space in the sewer network for it.
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Sussex – Sealed 20km of pipes in West Sussex to keep groundwater out of the sewer system.
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Partnership working - Working with 8 councils across the region to install sustainable drainage in communities to manage rainwater run-off.
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Schools partnership – Sustainable drainage systems installed at nearly 100 schools have diverted over 120 million litres of rainwater and groundwater away from sewers.
Nick Mills, Director of Environment and Innovation at Southern Water, said:
“We’re on a really exciting journey to create cleaner rivers and seas for everyone in our region. Preventing more than 700 releases in the first year is a clear sign that our approach is working - and we’re now scaling up resources, accelerating projects and expanding our partnerships to go even further, faster.
“This is one of the most complex environmental challenges of our time, made harder by climate change, heavier rainfall and a growing population. But we’re determined to meet it head‑on. By working closely with local authorities, communities and partners across the South, we can deliver the healthier waterways and coastal environments our customers expect and deserve.”
Southern Water’s Clean Rivers and Seas Plan is an interactive map showing where action is being taken now and where further work is planned over the next five years and beyond.
A major highlight of our programme is the way we’re harnessing nature to reduce storm overflows - with most of our planned interventions using sustainable solutions.
The plan builds on two years of £45m Pathfinder Projects that tested the most effective ways to reduce storm overflows, from sustainable drainage, wetlands, and optimisation of our network.