The UK water industry explained without the spin

If you’ve seen a headline about sewage spills, you’ve probably been told one of two things: things are improving, or things are a disaster. Both can be true at the same time. And neither, on its own, tells you very much.

What a sewage spill actually is

Most UK sewer systems are combined sewers — they carry rainwater and household waste in the same pipe. When it rains heavily, that system gets overwhelmed. To stop sewage backing up into homes and streets, the network has release points called combined sewer overflows (CSOs) that discharge the excess into rivers or the sea when pressure builds too high.

These aren’t accidents. They’re a deliberately designed feature of infrastructure that was mostly built before anyone expected current population density or current rainfall intensity. The discharge is diluted — but it’s still untreated wastewater, and the volume matters.

The actual problem

The problem isn’t that CSOs exist. It’s that they’re discharging far more often than they were designed to. The reasons are structural: ageing infrastructure, population growth, and increasingly intense rainfall events packing more water into systems that weren’t built to handle it.

None of that is particularly controversial. Where it gets complicated is the data.

Why the headline numbers are often misleading

You’ll regularly see claims like “spills reduced by 24%.” That sounds like progress. But that number, on its own, doesn’t tell you much. It could reflect a dry year — fewer rainfall events means fewer overflow triggers, regardless of whether anything structurally changed. A water company can cut its spill count in half just because it rained less.

It could also reflect changes in monitoring. More sensors mean more events get recorded, which can make figures look worse even when operational performance has improved. Fewer sensors, predictably, does the opposite. And counting the number of spill events isn’t the same as measuring their environmental impact — you can reduce event count while total discharge hours go up, or vice versa.

A number can go in the right direction without anything actually getting better. That’s the trap most reporting falls into.

The investment shortfall — and who created it

There’s a version of the campaigner argument that goes: water companies extracted dividends while infrastructure rotted. That’s not false. But it’s also incomplete without mentioning the regulator’s role.

For most of the period since privatisation, Ofwat’s price determinations — the five-yearly reviews that set what companies can charge — deliberately kept bills low. Political pressure and consumer protection goals made below-inflation increases the norm. The effect was a constrained funding envelope: companies simply didn’t have the allowed revenue to finance the scale of network upgrades that ageing combined sewers required.

This isn’t a defence of how companies allocated the money they did have, or of the dividend decisions that followed. But it does mean the story of why the network is in its current state isn’t purely one of boardroom greed. Ofwat spent decades trading off investment capacity against affordability — and the backlog of infrastructure work is partly the bill for that trade-off arriving.

Campaigners are right that investment was insufficient. They are sometimes less forthcoming about the fact that the regulator set the revenue limits that made higher investment structurally difficult.

The 2024 price review (PR24) has shifted direction significantly — allowing bills to rise by an average of around 26% over the 2025–2030 period, with the explicit aim of funding network improvements. Whether that capital actually flows into infrastructure rather than debt servicing remains to be seen.

So are things improving or not?

Sometimes yes. Sometimes no. Sometimes it just looks like they are because the weather cooperated. That’s the honest answer, and anyone who gives you something more definitive without explaining the context is glossing over the complexity.

To be fair, real infrastructure investment is happening — storage expansion, network upgrades, monitoring improvements. That work exists and it isn’t trivial. But investment doesn’t automatically translate to measured environmental improvement, and the gap between a press release about capital spending and actual performance data can be significant.

The questions worth asking

Whenever you see a performance claim, there are three questions that matter: compared to what baseline? Adjusted for weather? Does the metric being measured actually reflect what you care about environmentally?

If the answer to any of those is “unclear,” the number isn’t really telling you what it appears to be. Most reporting doesn’t ask them. That’s exactly what our improvement methodology is designed to address.

Where Water Watch fits in

Water Watch exists to slow this down. To take the reported numbers and the claimed improvements and ask: does this hold up? Sometimes it does. Sometimes it really doesn’t. We try to be honest about both.

The underlying data is public — it comes from official EDM sensor networks, regulatory reports, and the water companies’ own submissions. We don’t have any special access. We just look at what’s already there, properly. For a deeper look at how we work, read the Water Watch explainer.

Frequently asked questions

Don’t assume a better number means a better outcome. In this space, that link is often weaker than it looks — and it’s worth knowing why before you take any headline at face value.