Emergency Overflows: What the Water (Special Measures) Act Requires, and How to Detect a Discharge Within the Hour
TL;DR: The Water (Special Measures) Act 2025 adds a new duty to the Water Industry Act 1991. When an emergency overflow discharges, the sewerage undertaker must publish that it happened, where, and when it started within an hour of it beginning, then when it ended within an hour of it ending. The Act defines emergency overflows by four failures: power failure and mechanical breakdown at sewage works, rising main failure, and a blocked sewer downstream of the works. Publishing within the hour is impossible without detecting within minutes.
Last updated: 17 September 2026
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Key takeaways
- The Water (Special Measures) Act 2025 received Royal Assent on 24 February 2025. Section 4 inserts a new chapter on emergency overflows into the Water Industry Act 1991.
- When one of these overflows discharges, the undertaker must publish that it happened, where, and when it began within an hour, and when it ended within an hour of it ending.
- The Act defines emergency overflows by four events: power failure at sewage works, mechanical breakdown at the works, rising main failure, or a blockage downstream of the works, plus overflows identified as such in their permits.
- Section 4 starts on a date set by regulations. legislation.gov.uk does not yet show it in force, while the pollution incident reduction plan duty has applied in England since 23 June 2025.
- A one hour publication duty means detection in minutes. Level in the overflow chamber, pump status and rising main pressure are the signals that make it possible.
What are emergency overflows?
Emergency overflows are outlets in a sewerage system that discharge sewage to rivers, groundwater or the sea when something fails, rather than when it rains. Storm overflows relieve the system in wet weather. Emergency overflows protect it when a pump stops, a main bursts or a sewer blocks, which makes their discharges less predictable and often more serious.
The Water (Special Measures) Act 2025, section 4 gives the term a legal definition in a new section 141G of the Water Industry Act 1991. An overflow is an emergency overflow if it is part of an undertaker’s sewerage system, discharges into inland waters, underground strata or the sea, and discharges because of one of four events:
- Electrical power failure at sewage disposal works.
- Mechanical breakdown at sewage disposal works.
- Rising main failure.
- Blockage of a sewer downstream of sewage disposal works.
An overflow also counts where its environmental permit identifies it as an emergency overflow, or authorises its use in those circumstances. The definition matters because it decides which outlets count as emergency overflows under the new publication duty.
What does the Act require when emergency overflows discharge?
Publication within the hour. New section 141F requires the sewerage undertaker to publish that a discharge has happened, the location of the overflow, and when the discharge began, all within an hour of it beginning. When the discharge ended must follow within an hour of it ending.
The information must be in a form the public can readily understand and published so that it is readily accessible. The duty is enforceable under section 18 of the Water Industry Act 1991 by the Minister, or by Ofwat with the Minister’s consent or general authorisation, and ministers may make regulations for exceptions, for example by type of overflow, frequency of discharge or risk to water quality.
Timing is the open question. Under section 17 of the Act, section 4 comes into force on a day set by regulations, separately for England and Wales. At the time of writing, legislation.gov.uk records section 4 as not in force at Royal Assent, with no commencement shown since.
Our explainer on event duration monitoring covers the monitors already fitted to storm overflows, which is the natural comparison for what emergency overflows will need.
What else in the Act affects monitoring?
Beyond emergency overflows, three other sections change what undertakers must measure, prove and report.
| Section | What it does | In force |
|---|---|---|
| 3: pollution incident reduction plans | an annual plan, published before 1 April, approved personally by the chief executive | England 23 June 2025, Wales 1 September 2025 |
| 7: standard of proof | civil penalties for listed offences on the balance of probabilities | Royal Assent |
| 8: automatic penalties | the Environment Agency must impose fixed penalties for specified offences, save exceptions | Royal Assent |
Section 3 requires each plan to address how often pollution incidents happened in the previous year, how serious they were and why, the maintenance of the structures that caused them, and the measures planned, with their expected impact and timing. Our post on pollution incident reduction plans looks at how that evidence is gathered.
Section 8 changes the default on penalties. Where the Environment Agency can impose a fixed monetary penalty for a specified offence, it must do so, unless it considers there are exceptional circumstances or other enforcement action is in hand. Section 6 separately makes impeding an Environment Agency investigation of a water company punishable by up to two years in prison.
How do you detect a discharge from emergency overflows within the hour?
By watching for the failures as well as the spill. Each of the four events in the definition has a measurable signal that appears before or as the overflow operates, and a continuous signal with an alarm turns a one hour publication duty into a routine task rather than a scramble.
| Event in the Act | Signal to monitor | Typical measurement |
|---|---|---|
| Power failure at works | loss of supply, pumps stopped | power and pump status |
| Mechanical breakdown | pump fault, wet well level rising | pump status and level |
| Rising main failure | pressure drop, flow mismatch | pressure and flow |
| Downstream blockage | level rising upstream | level in chambers |
| The discharge itself | level above the overflow weir | level in the overflow chamber |
Level in the overflow chamber is the most direct of these, because it shows the discharge rather than its cause. The AQUAIOT Radar measures level without contact, to within ±2 mm, and reads reliably through foam, vapour and condensation in enclosed underground chambers. Mounted over the weir, it records when the level crosses the crest and when it falls back, the start and end times the duty asks for.
The causes behind emergency overflows deserve their own monitors. Our guides to pumping station monitoring and rising main burst detection cover the pump, pressure and flow side, and our guide to sewer blockage detection covers the rising levels that come before a blockage overflows.
Does the Act apply to private pumping stations?
The publication duty in section 141F applies to sewerage undertakers, not to private owners. But the four failures that define emergency overflows are the same ones that stop a private pumping station on a housing estate, business park or campus: a power cut, a failed pump, a split rising main or a blocked sewer.
Private owners already carry responsibility for their own stations, and a spill from one is still pollution. Our answer on who is responsible for a private pumping station sets out where that duty sits. The monitoring logic of the Act, detect the failure fast and record the discharge precisely, is simply good practice for any owner.
Frequently asked questions
What is an emergency overflow?
An overflow in a sewerage undertaker’s system that discharges to inland waters, groundwater or the sea because of power failure or mechanical breakdown at sewage works, rising main failure, or a blockage downstream of the works, or one identified as an emergency overflow in its permit.
How quickly must emergency overflow discharges be published?
Within an hour of the discharge beginning for the fact, location and start time, and within an hour of it ending for the end time, under new section 141F of the Water Industry Act 1991 inserted by the Water (Special Measures) Act 2025.
Is the emergency overflow duty in force?
Section 4 comes into force on a day set by regulations. At the time of writing, legislation.gov.uk shows it as not in force at Royal Assent, with no commencement recorded. The pollution incident reduction plan duty has applied in England since 23 June 2025.
What are automatic penalties under the Act?
Where the Environment Agency can impose a fixed monetary penalty on a water company for a specified offence, section 8 requires it to do so unless there are exceptional circumstances or other enforcement action is in contemplation or in progress.
Does the Act cover private sewage pumping stations?
The publication duty applies to sewerage undertakers. Private owners are not covered by it, but their stations fail in the same four ways, and monitoring level, pumps and rising mains detects those failures just as early.
Where to start
List the emergency overflows that fit the Act’s definition and, for each one, write down which signal would show its failure first: level, pump status, pressure or flow. Any overflow with no signal at all is a discharge that can only be found by someone passing by.
Then instrument the weir and the most likely cause together, and set alarms that route to someone who can publish and respond within the hour. Speak to an AQUAIOT engineer about level, pump and rising main monitoring for emergency overflows and the stations behind them.