Q.01

What is a combined sewer overflow?

A combined sewer overflow (CSO) is a release of untreated wastewater straight into a river, lake or coastal water from a combined sewer. A combined sewer is a single pipe that carries both sewage and rainwater runoff. In heavy rain, or when the system fails, the flow is more than the pipes or treatment plant can handle, so the excess goes out untreated. The EU recast Urban Wastewater Treatment Directive calls this a "storm water overflow" and defines it as "discharge of untreated urban wastewater into receiving waters from combined sewers caused by precipitation or system failures" [1].

Approach: I checked the definitions in Directive (EU) 2024/3019 (the recast Urban Wastewater Treatment Directive) and the US Clean Water Act (33 U.S.C. chapter 26, 2023 edition).

Key terms in Article 2 of Directive (EU) 2024/3019 [1]:

  • Combined sewer: "a single conduit that collects and conducts urban wastewater, including urban runoff."
  • Urban runoff: "precipitation in agglomerations collected by combined or separate sewers."
  • Separate sewer: a pipe that carries only one stream, for example domestic wastewater or urban runoff. Separate systems avoid the overflow problem that combined sewers have.

How US law handles it. The parts of the Clean Water Act I found don't give a stand-alone definition of CSO. They describe it as a discharge "from a municipal combined storm and sanitary sewer." Any NPDES permit, order or decree issued after December 21, 2000 for such a discharge must follow EPA's Combined Sewer Overflow Control Policy, signed April 11, 1994 (33 U.S.C. 1342(q)) [2]. That policy's "nine minimum controls" and long-term CSO control plans are also priority criteria for federal grants. The grants cover treatment works for CSOs and systems that tell the public when overflows release sewage into rivers and other waters (33 U.S.C. 1301) [3].

If you need it, I can go next into how the recast Directive controls these overflows through its integrated urban wastewater management plans (Article 5), or look up overflow discharge consents in the Environment Agency's register for England.

Q.02

How do I check sewage spills near me in England?

In England there are three official places to check: your water company's own storm overflow map for live spills, the Environment Agency's annual spill data for each overflow's history, and the Environment Agency's register of discharge permits to find which overflows are near you.

Approach: I searched the Environment Agency's water discharge consents register. Spill data isn't in the datasets I can search, so I used official GOV.UK and legislation.gov.uk pages for the rest.

1. Live spills: your water and sewerage company's map

  • Section 81 of the Environment Act 2021 added section 141DA to the Water Industry Act 1991. Under it, sewerage companies in England must publish that a storm overflow is spilling, where it is and when it started, all within an hour of the spill beginning. They must also publish when it stopped, within an hour of it ending. The information has to be "readily accessible to the public" and in a form the public can "readily understand" (legislation.gov.uk, s.81).
  • So start with the storm overflow map on the website of the company that handles sewage where you live. This is the company that runs your sewers, which may not be the company that supplies your drinking water.

2. Past spills for each overflow: Environment Agency annual returns

  • The Environment Agency publishes "Event Duration Monitoring – Storm Overflows – Annual Returns". It shows how often and for how long each monitored overflow spilled each year, with one sheet for each of the 10 sewerage companies.
  • It covers 2020 to 2025, with long-term trends back to 2016. You can view it on an interactive map or download it as Excel files under the Open Government Licence.
  • It was last updated on 18 September 2026; the August 2026 revision corrected the Anglian Water and Northumbrian Water data (data.gov.uk).

3. Which overflows are near you: the discharge consents register The Environment Agency's register lists each permitted overflow with its operator, address, postcode, grid reference, local authority and permit dates. You can search it by postcode or local authority. Three examples:

  • Worple Road CSO, London SW20 8QA (Merton), Thames Water, permit TH/TEMP.3044/003, in force since 30 March 2020 [4]
  • Milton St Combined Sewer Overflow, WS2 9EG (Walsall), Severn Trent, permit MI/TSC1302/001 [5]
  • Mafeking Combined Sewer Overflow, Morpeth NE61 2SW, Northumbrian Water, permit NE/EPRAB3196VY/001 [6]

Look at the revocation date before relying on an entry. Many entries are old permits that have since been replaced or withdrawn, such as Egerton Road Storm Overflow in Bexhill, revoked on 14 June 2024 [7].

If you see sewage in the water GOV.UK says water pollution "includes sewage or spills in places such as the sea, rivers, lakes, streams or canals". You report it through the online Report water pollution service. The Environment Agency's 24-hour incident hotline is 0800 80 70 60 (GOV.UK).

If you give me your postcode or local authority, I can list the storm overflow permits near you that are still in force.

Q.03

What permit lets water companies discharge from them?

A storm overflow discharge in England needs an environmental permit for a "water discharge activity" under the Environmental Permitting (England and Wales) Regulations 2016. The Environment Agency issues these permits. Each overflow has its own permit, and the permit's conditions set when and how it may spill. Regulation 12 says a person must not "cause or knowingly permit a water discharge activity" except "under and to the extent authorised by an environmental permit" [8].

Approach: I read the current revised text of the 2016 Regulations and checked how storm overflow permits appear in the Environment Agency's water discharge consents register for England.

Why storm overflows are covered

  • Under Schedule 21, a "water discharge activity" includes the discharge or entry of "trade effluent or sewage effluent" (and any "poisonous, noxious or polluting matter") into inland freshwaters, coastal waters or relevant territorial waters [9]. Storm sewage spilling from a combined sewer falls inside that definition.
  • The permit requirement does not apply if the activity is an exempt facility (regulation 12(2)) [8].

Who is responsible for the discharge

  • Schedule 21, paragraph 6 deals with sewage effluent from a public sewer. The sewerage undertaker that owns the sewer (the "discharging undertaker") is treated as causing the discharge of matter it received and was bound to receive [9].
  • If another undertaker sent the sewage in through a main connection under an agreement made under section 110A of the Water Industry Act 1991, that "sending undertaker" is the one treated as causing it [9].
  • There is one defence for England (paragraph 6(5A)). A sewerage undertaker is not guilty of an offence under regulation 38(1) or (2) if all three of these apply:
    • the breach comes from something another person put into the sewer;
    • the undertaker was not bound to accept it, or was bound only on conditions that weren't met;
    • the undertaker could not reasonably have prevented it [9].

How these permits appear in the register In the Environment Agency's register, these entries have site type "Combined Sewer Overflow" and effluent type "Sewage - Storm Sewage". Some are old permits that are still in force, and some were issued recently:

  • Mafeking Combined Sewer Overflow, Northumbrian Water, NE/EPRAB3196VY/001, start date 3 February 2014 [6]
  • Fairlee Combined Sewer Overflow, Southern Water, SO/NPSWQD000451/003, start date 17 October 2025 [10]
  • Victoria Avenue Storm Combined Sewer Overflow, Severn Trent, MI/S/02/21018/O/002, start date 31 March 2026 [11]

The permit is separate from the duty to publish spill information within an hour, which I covered last time. That duty comes from the Water Industry Act 1991 as amended by the Environment Act 2021, not from the permit.

I can pull the full permit record for a particular overflow next, or look for Environment Agency enforcement actions against a sewerage company for breaking its permit conditions.

Q.04