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We're investing in river health

We want to do the right thing for our watercourses and the communities that love them. So, we've got a plan to reduce harm to river water quality.

Our river health report

In April 2022 we set out our first river health action plan, describing how we planned to improve the health of rivers in the Thames catchment. One year on, we've updated the plan to let you know about our progress and plans going forward. You can read more in our river health report.

We're aiming to:

  • Discharge higher-quality treated effluent that meets all required standards
  • Reduce potentially polluting discharges to our rivers
  • Work with partners to improve river water quality 

We’re also looking forward to sharing our PR24 plan, which will indicate our direction of travel to reach governmental targets of no more than 10 discharges on average, per overflow per year by 2050. We’re planning for: 

  • Maximum of 24 spills on average, per overflow per year by 2025 
  • Maximum of 17 spills on average, per overflow per year by 2030

Higher-quality treated effluent discharges

Treated sewage effluent is an important source of flow in many of our rivers and streams. Without it, many of them would run dry in the summer months. So, we have to make sure our sewage treatment works (STW) are performing as they should be.

We monitor our STW, upgrading them where needed. This makes sure that they continue to treat incoming flow to the required standards. When the treated effluent is discharged, rivers and streams should be adequately protected. 

A view across Mogden sewage treatment works

We also work with local authorities to understand their housing projections. This means we can upgrade sewage treatment infrastructure before development completes.  

As the population increases so does the amount of wastewater arriving at STW. This adds more nutrients (nitrates and phosphorus) into our rivers than they can cope with. By 2020 we reduced phosphorus levels by 74%. Our current plans will take this to 80% in the first years of our next business plan period, which starts in 2025.

Reducing the use of storm overflows

We think any discharge of untreated sewage is unacceptable, even when it’s legally permitted. So, we’re taking initial steps to make the use of storm overflows unnecessary, and we’re being more transparent with our data as part of this journey. This includes the virtual elimination of sewage overflows in the Chess and upper Windrush catchments.

We're delivering the Thames Tideway tunnel, London's 'super sewer' and the biggest single overflow reduction project ever. The tunnel will prevent millions of tonnes of untreated sewage, mixed with rainwater, from entering the tidal reaches of the River Thames via storm overflows each year.

The Greenwich connection tunnel linking Greenwich pumping station to the main super sewer

In the rest of our area, we've developed a detailed programme for reducing the number of overflows from our sites. This includes removing surface and/or groundwater from our sewers in some cases. Our long-term aim is to get rid of all storm overflows.

Eliminating polluting discharges

Reducing pollution incidents is a priority for us. We're continuing to deliver targeted pollution reduction activities, such as:

  • replacing pumped sewer mains which have failed
  • reducing blockages by cleaning the sewers
  • customer education to prevent the incorrect disposal of products into sewers
  • building up our smart waste programme
  • upgrading our sewage treatment works for permit compliance

Our pollution incident reduction plan (PIRP) is updated annually.


Working with partners

Working effectively with partners is key to delivering environmental solutions that give greater benefits than simply addressing our own issues. As part of the next business planning period, we have submitted an ambitious programme called ‘Rethinking Rivers’ to the Environment Agency. It will put this into practice at a large scale and build on the successes of our three Smarter Water Catchments (SWC) trials currently underway.

A good example to bring to life our partnership approach is the challenge we face with surface water drains being misconnected with foul drainage. Since 2016, we have been funding the Zoological Society of London (ZSL) to run ‘Outfall Safaris’ with interested catchment partners. These safaris identify surface water outfalls serving urbanised areas with signs of pollution with assistance from volunteers to identify and address misconnections and other potential widespread pollution sources. We pass these to our pollutions team for immediate action. This leading approach is now being replicated nationally.


Two people walk alongside river carrying binoculars while their dog runs in front

Next steps

During the final two years of this investment period, we are spending £1.12 billion on our sewage treatment plants. This includes £650 million on enhancing and upgrading over 135 existing sites to improve resilience and provide additional capacity. Over the same period, we'll spend a further £470 million on the wider sewer network.

This is a live plan which is kept under continual review. This ensures it addresses the highest priority issues for maintaining and enhancing river water quality through improvements to our wastewater systems and the way we operate them. As such, this report is a snapshot in time and we expect our plans to evolve as our understanding of the issues affecting river water quality and the most effective ways to reduce harm develops.

Storm overflow action plan

In March 2024 we published our storm overflow action plan. This is requested by Defra from every water and sewerage company in England. We’ve also published an accompanying guide to help explain the data in more detail. It includes assessments and interventions for reducing the use of 620 storm overflows. The document outlines how we will deliver against governmental targets. This includes discharging, on average, no more than 10 times per overflow, per year.

Like the river health action plan, the storm overflow action plan should be considered a working document, rather than a final plan. It will also be subject to change as our planning evolves.

See our improvement plans for specific locations.