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Environment Act 2021 — Storm overflows

Environment Act 2021 introduces new duties on undertakers helping to reduce the problem of storm overflows discharging into aquatic surroundings.

The Environment Act sets out a requirement for sewerage undertakers to secure a progressive reduction in the adverse impacts of storm overflow discharges, while the Plan sets out clear and unambiguous requirements upon water companies and the government.

The Environment Act 2021 — new measures and proposals

  • a duty on the government to publish a plan by September 2022 to reduce the frequency, duration and volume of sewage discharges from storm overflows and also the adverse impacts on the environment and public health of such discharges
  • a duty on government to report to Parliament on progress made in implementing the plan and its effects, the first report to cover the first three years of the plan and subsequent reports to cover periods of five years
  • duties on sewerage companies and on the Environment Agency to publish data on storm overflow operation, including the location of storm overflows, frequency, duration and (if available) volume of discharges in the period covered by the report, the receiving watercourse, and (for sewerage companies) information on investigations and improvement works carried out. Each report must relate to a calendar year, starting with 2021.

Since that time the storm overflow provisions within the Bill have been significantly added to by the House of Lords, then amended on a number of occasions during the consideration of amendments in each House. 

The measures outlined above have remained and are in the Act, but with the addition of further measures, detail of which we set out below.

The Environment Act 2021 sets out a requirement for sewerage undertakers to secure a progressive reduction in the adverse impacts of storm overflow discharges, while the Plan sets out clear and unambiguous requirements upon water companies and the government.

Reporting on discharges from storm overflows

When a storm overflow discharge occurs, the sewerage undertaker must publish, within an hour of the discharge beginning, that there has been a discharge, its location and when it began. A second publication must take place, within one hour of the discharge ending, stating when the discharge ended.

This information must be published in a form that allows the public readily to understand it and is readily accessible to the public.

The Act also empowers the Secretary of State to prescribe exceptions from these duties, by regulations. Examples of the criteria for such exceptions are by reference to descriptions of storm overflows, frequency of discharge or level of risk to water quality. Draft regulations must be approved by both Houses of Parliament.

Water quality monitoring

Sewerage undertakers will be required to continuously monitor the quality of water both upstream and downstream of storm overflows and sewage disposal works, where the asset discharges into a watercourse. The data required to be gathered is the level of dissolved oxygen, temperature, pH, turbidity, ammonia level and anything else specified in regulations.

Regulations will also provide details on how the monitoring is to be carried out, including the types of monitor and where they should be placed, and may require undertakers to publish the monitoring data. Again, the Secretary of State may prescribe exceptions from these duties by regulations, for example by reference to descriptions of asset, frequency of discharge or level of risk to water quality. 

Reduction of adverse impacts of storm overflows

The Act places a duty on sewerage undertakers to secure a progressive reduction in the adverse impacts on the environment and public health of discharges from storm overflows.

The Act makes no mention of how “progressive reduction” is to be interpreted.

When does the Environment Act 2021 come into force?

The ‘original’ measures will come into effect two months from 9 November 2021 (the day on which the Act was passed).

The ‘new’ measures will take effect on dates to be appointed by regulations.


The Environment Act states that references to discharges from a storm overflow do not include discharges that occur as a result of:

  • electrical power failure at sewage disposal works
  • mechanical breakdown at sewage disposal works
  • rising main failure
  • blockage of any part of the sewerage system downstream of the storm overflow

Enforcement of the Environment Act 2021

The duties imposed on sewerage undertakers will be enforceable by the Secretary of State or by Ofwat (in accordance with a general authorisation given by the Secretary of State) by means of an enforcement order pursuant to section 18 Water Industry Act 1991

Storm overflows discharge reduction plan

Actions for water companies

The Plan sets out ambitious targets requiring water companies to participate in a mandatory £56bn investment project to fix the long-standing issue of storm overflow discharges. Two clear targets are:

  • By 2035, water companies must have improved all overflows discharging into or near all designated bathing water, and improved 75% of those discharging to high-priority sites
  • By 2050, no storm overflows will be permitted to operate outside of unusually heavy rainfall or cause any adverse ecological harm

In addition to setting headline targets and sub-targets, the Plan sets out seven principles that the Government expects water companies to adhere to when achieving those targets. These principles should not be overlooked; imposing important requirements that water companies will want to be able to substantiate when subject to the Regulatory “support and challenge” process envisaged by the Government.

Actions for Government

The Plan also sets out actions that the Government has committed to take, including:

  • Improving transparency — passing secondary legislation to implement requirements of the Environment Act in respect of the publication of information by water companies and guidance on monitoring the water quality impact of their assets.
  • Proposals for the better management of rainwater — including the promise of a decision regarding the implementation of new standards for sustainable drainage systems (SuDS) in England and removing the automatic right to connect to the public sewer system.
  • Ongoing work to review and implement findings of the Storm Overflows Taskforce.
  • Work to deliver the Surface Water Management Action Plan.
  • A review of the Bathing Water Regulations 2012 to protect bathers and other recreational water users.
  • Action to improve protections for shellfish waters.


The Government will be required to report on progress in respect of the Plan, with a report on its implementation due in 2025 and further mandatory review in 2027.

Progress against this plan will also be scrutinised by Ofwat, the economic regulator for the water industry, and the EA, the environmental regulator in England. Both regulators are expressly supported in the role that they will play in respect of Storm Overflows, enabled by strengthened monitoring and reporting requirements, including:

  • 100% coverage of storm overflows through Event Duration Monitoring (EDM) by 2023, requiring water companies to report the frequency and duration of spills
  • Storm overflow data to be published annually, with frequency and duration data required in near real time
  • Monitoring the water quality impact of assets that discharge sewage into river systems

The passing of the Environment Act 2021 and the publication of the Storm Overflows Discharge Reduction Plan (the Plan), marks a watershed in the industry’s approach to the issue.

For further information or to find out how we can assist you, contact our specialist environmental lawyers.