Rising main bursts: the failure the pump hides for you

TL;DR. A rising main is the one sewer asset that is pressurised, buried and continuously loaded, which is why it fails badly and quietly. Of the 75 serious pollution incidents recorded for water and sewerage companies in England in 2024, the Environment Agency attributes 15 to rising mains. There is nothing to see on the surface until there is a great deal to see, so detection has to happen at the pumping station rather than along the pipe.

Key takeaways

• The Environment Agency recorded 75 serious pollution incidents, category 1 and 2, for water and sewerage companies in England in 2024.
• That was a 60% increase from 47 in 2023.
• Rising mains account for 15 of those 75, behind foul sewers at 22 and treatment works at 20.
• Foul sewers, treatment works, rising mains and pumping stations together represent 68 of the 75, or 91%.
• The pipe is pressurised, so a defect discharges continuously rather than surcharging visibly.
• Section 94 of the Water Industry Act 1991 requires a sewerage undertaker to cleanse and maintain sewers so the area continues to be effectually drained.

Last updated: 4 September 2026

What is a rising main and why does it fail differently?

A rising main is the pressurised pipe that carries sewage from a pumping station up to a point where gravity can take over again. Everything else in a foul network runs part-full under gravity. This one runs full, under pressure, every time the pump starts.

That single difference changes every failure mode. A gravity sewer with a defect leaks slowly or lets groundwater in. A pressurised main with a defect pushes sewage out under pressure, continuously, for as long as the pump runs. There is no surcharging manhole to notice and often nothing at ground level at all, because the discharge finds its way into made ground, a land drain or a watercourse.

It is also the asset with the fewest inspection options. You cannot put a camera through a live main, and taking it out of service means the wet well upstream starts filling immediately. Condition assessment is therefore rare, expensive and disruptive, which in practice means it does not happen often.

How much of the pollution problem is rising mains?

A fifth of the serious end of it. The Environment Agency’s environmental performance report for 2024 records 75 serious pollution incidents, category 1 and 2, across water and sewerage companies in England, a 60% increase from 47 in 2023.

Within that total, the report states that the majority of serious pollution incidents continue to be from foul sewers (22) followed by treatment works (20), rising mains (15) and pumping stations (11), representing 68 out of the 75, or 91%.

Two caveats are worth stating plainly. That dataset covers water and sewerage companies in England, not private networks, so it is not a national total across all owners. And rising mains are a small fraction of total sewer length, which makes 15 of 75 a disproportionate share rather than a proportionate one.

The same report attributes performance problems partly to long-standing issues with underinvestment and poor maintenance of assets, and to an ageing network that is not resilient to pressures from extreme weather.

Why does a rising main burst go unnoticed?

Because the system compensates for it before anyone sees it. The pump does not know the pipe has failed. It knows the wet well is filling, so it starts, and it keeps running until the level drops. If a proportion of the flow is leaving through a defect, the level still drops, just more slowly, and the pump simply runs longer.

1. A defect opens and part of the flow leaves the pipe under pressure.
2. The wet well takes longer to empty, so run time per cycle increases.
3. Discharge pressure at the pump falls, because the pipe is no longer sealed.
4. Cycles become more frequent as the effective capacity of the main drops.
5. Nothing at ground level changes until the escape finds a surface route.

Every one of those first four is measurable at the pumping station, on the dry side, rather than inside the wet well itself, which HSE treats as a confined space. That is the whole opportunity. You cannot inspect the buried pipe, but you can watch the machine that pushes water through it, and the machine changes behaviour long before the ground does.

What should you actually monitor?

Three signals, and the relationship between them matters more than any one alone. Wet well level, pump run time per cycle, and volume delivered per cycle. A change in any one has innocent explanations. A change in the relationship between them does not.

AQUAIOT Radar handles the level side without contact, at 60 GHz and accurate to within ±2 mm, reading through the foam, vapour and condensation that defeat float switches and ultrasonic units in a wet well. ATEX variants are available where the chamber requires them, and because nothing is submerged there is nothing to foul, which matters on an asset where fouling is the normal state.

On the delivery side, the Clamp-on Ultrasonic Flow Meter reads flow and total volume from the outside of the pipe, across DN8 to DN100, without cutting into a pressurised main. That is not a preference on a rising main. Breaching a live pressurised sewer to fit an insertion meter is a job nobody wants and a permit nobody enjoys writing.

AQUAIOT’s sewer monitoring service applies the same sensing across wet wells, rising mains, manholes and overflows, reporting over encrypted cellular and LoRaWAN into the AQUAIOT Cloud with threshold alarms, trendlines and exports, plus RS485 and Modbus on site and open APIs into SCADA and asset management systems.

What is the duty behind all this?

For a public network, section 94 of the Water Industry Act 1991. A sewerage undertaker must provide, improve and extend such a system of public sewers and so cleanse and maintain those sewers as to ensure that that area is and continues to be effectually drained.

Effectually drained is an outcome test rather than an activity test, which is the same distinction that runs through most of this. A maintenance schedule describes what you did. A run-time trend describes whether the asset is still doing what it is there to do.

For a private pumping station on an estate, a campus or a development, there is no equivalent statutory undertaker duty, which cuts both ways. Nobody else is watching it, and the consequences of a failure land on the landowner rather than on a company with an incident response function.

From our sister company: Choosing a cellular router for the kiosk? Indiott compares Milesight and Teltonika routers model by model.

Frequently asked questions

How do you detect a rising main burst?

Not by looking at the pipe, which is buried and pressurised. You detect it at the pumping station, by watching pump run time per cycle, discharge pressure and the volume delivered per cycle against wet well drawdown. A main losing flow through a defect makes the pump work longer for less delivered volume, and that divergence shows up well before anything surfaces.

Why are rising mains such a large share of serious incidents?

Because pressure turns a small defect into a continuous discharge, and the asset is almost never inspected. The Environment Agency attributes 15 of the 75 serious pollution incidents recorded for water and sewerage companies in England in 2024 to rising mains, despite them being a small proportion of total sewer length.

Can you put a CCTV survey through a rising main?

Not while it is live. Surveying one means taking it out of service, and the wet well upstream begins filling from the moment you do, so the work runs against a clock and usually needs over-pumping or tankering. That cost and disruption is precisely why condition data on rising mains is so thin, and why indirect monitoring is worth more here than on almost any other asset.

Does this apply to private pumping stations?

Yes, and arguably more so. The physics is identical, the asset is usually smaller and older, and there is no statutory undertaker watching it. On a private site the first indication of failure is often a wet area of ground, a smell, or a pollution report from somebody else.

Where to start

Baseline one pumping station for a month. Establish the normal run time per cycle, the normal number of cycles per day and the normal relationship between run time and level drawdown, in dry weather. That baseline is the entire diagnostic, and until it exists a lengthening run time is just a number nobody can interpret.

The asset you cannot inspect is the one worth instrumenting first. Speak to an AQUAIOT engineer about levelling the wet well and metering the delivery side on your rising main.

By GP, Digital and IoT lead at AQUAIOT.