Skip to main content

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 original measures

We have reported previously on measures in the Environment Bill, during its passage through the House of Commons, to curtail the use of storm overflows. Those measures could be summarised as consisting of:

  • 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 new measures

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.


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 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.


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.


The duties imposed on sewerage undertakers apply to undertakers whose area is wholly or mainly in England.


Not only the public but also undertakers may be pleased that these duties have been enacted. They will help to reduce the long-standing situation of storm overflow discharges to the aquatic environment, a situation which the undertakers themselves have long regarded as unacceptable but did not have the necessary statutory and regulatory framework to enable the implementation of significant remedial steps. The measures within the Act set out that framework, albeit subject yet to further detail in regulations. However, a substantial unknown remains in respect of “progressive reduction in the adverse impacts of discharges from … storm overflows”, both in terms of the precise meaning of this duty, how it is to be achieved and the time period for doing so. To that extent, the Act is merely the starting point.

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