1. What are storm overflows?

Storm overflows are “safety valves” used in combined sewer systems to protect properties from overloaded sewers causing flooding and sewage backing up into streets and homes during heavy storm events. They are used to spill excess wastewater and rainwater into inland waters and the sea. The overflow discharges can also occur at wastewater treatment facilities. There are around 15,000 storm overflows in England and approximately 13,350 of those discharge to inland rivers.

Storm overflow discharges happen when the sewerage system is at risk of being overwhelmed. Surges in flow usually occur in wet weather because of the extra volume of water passing through the sewer network. However, they can also be caused by a misuse of the system, such as people sending wet wipes, fats and grease into the network. These clog up the pipes and reduce their capacity. The storm overflow releases are normally dilute compared to wastewater, with a very high rainwater content. They may also be screened to remove litter. However, they are untreated and contain raw sewage which has high levels of harmful pathogens, such as viruses and bacteria.

The Environment Agency (EA) regulates discharges from storm overflows by issuing environmental permits for individual storm overflows. The permits outline when they can be used, as well as how they should be monitored and managed. The EA has a range of enforcement duties, including civil sanctions such as fixed monetary penalties and compliance notices. Ofwat is the independent economic regulator of the water companies. It can issue enforcement orders to ensure storm overflow discharges comply with the law. Ofwat can also impose financial penalties on water companies if they are in breach of their statutory duties or licence conditions.

2. How often do storm overflow discharges occur?

Increases in population, hard surfaces, and more frequent and heavier storms have increased pressure on the sewage system, bringing the “frequency of discharges to an unacceptable level”, according to the government. Data collected by the EA shows that the average number of spills per overflow increased between 2017 and 2019. However, between 2019 and 2021 these figures reduced slightly but remained much higher than in 2017. This is illustrated in the chart below.

Chart 1: Storm overflow spills in England between 2016 and 2021: Average number of events and duration

Chart shows the average number of spills per storm overflow, and average duration (in hours) of each spill event per overflow, in England over the period 2016 to 2021.

(Department for Environment, Food and Rural Affairs, ‘Event duration monitoring: Storm overflows: Annual returns: Long-term trends’, 31 March 2022. Data is provided by water and sewerage companies to the EA each year as part of their regulatory annual return.)

Data published by the EA in 2021 showed that:

  • The average number of spills per storm overflow was 29 in 2021, compared to 33 in 2020.
  • In 2021, 5% of storm overflows recorded 100 or more spills, compared to 8% in 2020.
  • In 2021, 13% of storm overflows did not spill. This number was the same as in 2020.
  • The average duration of each spill was seven hours in 2021, compared to an average of eight hours in 2020.

Monitoring of sewage spills from storm overflows and wastewater treatment plants has improved in recent years as event duration monitors (EDMs) have been rolled out across the network. Around 12,000 EDMs had been installed by water companies by 2020, providing data on over 80% of the sewerage network. By 2021, the percentage of storm overflows with monitoring devices had increased to 89%, amounting to 12,707 overflows. Complete coverage of the network is due to be completed by 2023.

Under the Environment Act 2021, water companies and the EA must publish monitoring data on storm overflows on an annual basis (see section 3 for further information).

Renewed concerns about the frequency and duration of storm overflow discharges were voiced after heavy rainfall in August and September 2022 resulted in numerous overflow discharge events releasing untreated sewage into rivers and the sea. Reports on data collected by the charity Surfers Against Sewage stated that pollution warnings were in place for more than 100 British beaches at the beginning of September 2022. In Parliament, several parliamentary questions were tabled asking the government what steps it was taking to ensure untreated sewage was not discharged into rivers and the sea. In response to an urgent question from Caroline Lucas (Green Party MP for Brighton, Pavilion) the then secretary of state for environment, food and rural affairs, George Eustice, stated that the government had set a “clear requirement” for water companies to reduce the harm caused by overflow discharges in the Environment Act 2021. Mr Eustice further explained that the storm overflows discharge reduction plan would start the “largest investment in infrastructure ever taken by the water industry”.

3. Government policy to reduce storm overflow discharges and their adverse impacts

The government has said it recognised there needed to be a “significant step change on action to protect public health and the environment” from storm overflow discharges. The government stated its policy was to implement a range of measures to reduce the frequency and harm of storm overflow spills.

The government introduced several of these measures under the Environment Act 2021. These included:

  • A new duty directly on water companies to secure a progressive reduction in the adverse impact of discharges from storm overflows.
  • A new duty on government to produce a statutory plan to reduce spills and their adverse impact, and report to Parliament on progress. The plan was required by 1 September 2022.
  • A requirement for government to produce a report setting out the actions that would be needed to eliminate spills from storm overflows in England, and the costs and benefits. The report was required by 1 September 2022.
  • A new duty placed on water companies and the EA to publish data on storm overflow operation on an annual basis.
  • A new duty directly on water companies to publish near real-time information on the operation of storm overflows.
  • A new duty directly on water companies to monitor the water quality upstream and downstream of storm overflows and sewage disposal works.
  • A new duty directly on water companies to produce statutory drainage and wastewater management plans. The plans must set out how the companies will manage and develop their drainage and sewer system over a minimum 25-year planning horizon, including how storm overflows will be addressed through these plans.
  • A power of direction for the government to direct water companies in relation to the actions in these drainage and sewerage management plans if they are not good enough. The government has said it will “not hesitate to use this power of direction”.

In February 2022, the government also set a “clear expectation” in the strategic priorities statement for Ofwat that the regulator should prioritise action by water companies to “significantly reduce storm overflows”, and that Ofwat should ensure funding to do so is approved.

4. Storm overflows discharge reduction plan

Under the Environment Act 2021, the government was required to publish, by 1 September 2022, a plan to reduce storm overflow spills and their adverse impact, and a report setting out a cost-benefit analysis of the actions needed to eliminate spills. The government stated it would “set clear and enforceable targets that the water industry must meet”. On 31 March 2022, the government launched a consultation on its storm overflows discharge reduction plan to seek views on the targets and its other core proposals. The consultation was open for 12 weeks and closed on 12 May 2022.

The main measures set out in the consultation included:

  • Time-bound targets for water companies to achieve the “complete elimination of ecological harm from storm overflows, further protect public health and limit storm overflow use”.
  • Details of how water companies will be expected to achieve these targets, such as: regulatory compliance; mapping sewer networks of overflows and separate rainwater pipes connected to the combined sewer network; reducing surface water connections to the combined sewer network; and proactively investigating “novel solutions”, making use of Ofwat’s innovation fund. Water companies will be expected to set out how they will meet their storm overflow targets in their drainage and wastewater management plans.
  • Commitments to revise guidance on how to make an application for new bathing water designation. The government said it would consider further steps to improve the timeliness and usefulness of information the public are given about water quality.

The storm overflows discharge reduction plan was published on 26 August 2022. It set out time-bound targets for water companies to reduce storm overflow spills, and included a report on the feasibility of eliminating discharges from storm overflows. Launching the plan, the government stated that it would require water companies to deliver £56bn capital investment over 25 years into a long-term programme to tackle storm sewage discharges by 2050. The government said the plan “frontloads action in particularly important and sensitive areas” including designated bathing waters and high priority ecological sites.

Under the plan, water companies are required to achieve a number of targets:

  • Water companies will only be permitted to discharge from a storm overflow where they can demonstrate there is no local adverse ecological impact. This target must be achieved for at least 75% of storm overflows discharging in or close to high priority sites by 2035; for all remaining storm overflows discharging in or close to high priority sites by 2045; and for all remaining storm overflow sites by 2050.
  • Water companies must significantly reduce harmful pathogens from storm overflows discharging into and near designated bathing waters by either applying disinfection or reducing the frequency of discharges to meet Environment Agency spill standards by 2035.
  • Storm overflows will not be permitted to discharge above an average of 10 rainfall events per year by 2050.

Failure of the water companies to meet these targets could result in fines or a requirement for them to return money to their customers.

The government will review these targets in 2027 to consider where it could go further, “taking account of innovation and efficiencies”.

The plan also set out several principles the government expects the water companies to adhere to when achieving the targets, including:

  • complying with existing regulatory obligations and duties
  • mapping their sewer networks, and understanding where properties with separate rainwater pipes are connected to their combined sewer network
  • clearly setting out how they will meet their storm overflow targets in their drainage and wastewater management plans
  • achieving year-on-year reductions in the amount of surface water that is connected to their combined sewer networks
  • considering treatment of sewage discharges as an alternative solution where appropriate
  • treating rainwater as a resource to be valued for the benefit of people and the environment
  • discharging rainwater back to the environment as close as possible to where it lands or channelling it to a close watercourse without first mixing it with sewage.

Water companies will be required to publish discharge information in near real time as well as “committing to tackling the root causes of the issue by taking steps to improve surface water drainage”.

The government concluded in its cost-benefit analysis on eliminating storm overflows spills that applying a policy of complete elimination nationally was “not feasible, or within the public interest, due to the financial and environmental costs”.

The government stated the targets outlined in the storm overflows discharge reduction plan aimed to “strike the right balance between the scale and pace of ambition, and the increase in consumer bills”.

5. Reaction to the plan

On 5 September 2022, when Parliament returned from its summer recess, the storm overflows discharge reduction plan was laid before both Houses. In a written statement to the House of Commons, the then secretary of state for environment, food and rural affairs, George Eustice, set out the intention of the plan:

This will start the largest investment in infrastructure ever undertaken by the water industry, an estimated £56bn of capital investment over the next 25 years. This will eliminate 80% of discharges by 2050.

Mr Eustice explained that the approach taken by the government was to “carefully balance our ambitions to improve and protect the environment with the need to limit the impact on consumers, particularly when households are facing pressures”. He stated the purpose of the mandatory review in 2027 was to evaluate any new evidence to see if it was “possible to go faster, without disproportionately affecting consumers”.

Speaking in the House of Commons about the plan, Shadow Secretary of State for Environment, Food and Rural Affairs Jim McMahon argued the plan was “not worth the paper it was written on”. Mr McMahon said the plan gave water companies the “green light to carry out another 4.8mn discharges through to 2035”. Caroline Lucas also criticised the timeframe of the targets. She questioned the “urgency” of the government’s response:

We have a so-called plan that allows water companies to continue polluting until 2035 in areas of significant importance to human and ecological health and until 2050 elsewhere, which means sanctioning nearly 30 more years of pollution. Is that genuinely what the secretary of state considers to be an urgent response?

In response, Mr Eustice said that long-term infrastructure changes and investments were necessary before other action could be taken:

We have to take decisions now, and invest in the infrastructure and the capacity to prevent such discharges from happening. Were we to do what the hon. Lady would like, which is to stop using these arrangements immediately, sewage would literally back up into people’s homes, and I am not sure that that is something they would thank us for. We must therefore have a programme of investment, and we are the first government to set this out.

There has also been criticism of the targets from stakeholders such as the conservation organisation the Rivers Trust. The trust said it was “disappointed by the targets set out in the plan”, and the “government’s lack of ambition and clarity for the sector. It argued:

Far from revolutionising the sewer system, as the plan claims, this plan aims to claw its way back to what should have already been ‘business as usual’ by 2050 with sewer overflows operating only during exceptional rainfall events by that time. This should be the current situation, and yet we are living with 2.6mn hours of overspills in England.

The trust’s director for policy and science, Rob Collins, stated it would continue to advocate the designation of further inland bathing waters; better management of rainwater; and ringfenced protection for sites of special scientific interest and special areas of conservation and chalk streams.

However, Water UK argued the plan represented a step forward. It said that water companies agreed there was an urgent need to do more, and companies were “ready to invest to achieve these ambitious plans”. Water UK advocated additional action from government, regulators and other sectors to bring about further environment benefits:

Government should close the loophole that allows housing developers the right to overload sewers and also take action on the flushed wet wipes that create the fatbergs that cause so many blockages. A greater focus on keeping rainwater out of sewers, via measures such as sustainable drainage, would also tackle the source of the problem and help bring about the transformation we all want to see.

Water UK represents water and wastewater companies across the UK.

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Cover image by Matthew Feeney on Unsplash.