In numbers

The live data and Welsh Water's own figures behind the front page, in plain text. Every day, Wales makes waste that can power homes and fertilise fields. Some of it still ends up in our rivers.

Important

Corrected, version 2.0.0. The first version of this site, and the briefing paper behind it, made claims that were wrong: that Welsh Water wastes its sludge, that there are 718,803 MWh of untapped energy, that the investment would pay for itself. Welsh Water already digests 98.2% of its sludge. We have kept the original and marked every claim we retired. What changed and why · The original, kept

Right now in Welsh waters

…

storm overflows report that they are operating right now, out of … that report their status to the public. About … more operated in the last 24 hours.

• operating now
• operated in the last 24 hours
• not operating
• bathing water: excellent
• good
• sufficient
• poor (2024 classification)

Source: Welsh Water's live overflow status service. The first version of this site read only the first 2,000 of its 2,362 records; it now reads all of them.

The worst sites in 2024

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Hours are summed over sites, so they are site-hours: many overflows can be spilling at once. The first version of this site called a sum like this years of sewage spilled, which it was not. The full list is Welsh Water's 2024 return.

What Welsh Water's own data shows

These come from the annual performance tables Welsh Water publishes for Ofwat. Each links to its source.

• 98.2% of its sewage sludge goes through advanced anaerobic digestion, which makes energy and fertiliser (2025-26). Source. We said the opposite on the first version of this site, and we were wrong. That is the company-wide share by weight: only 37.3% of the sludge is made at the four works that have a digester on site, and the rest is carried to them from the other works. How we got this Sludge is only the solids a works takes out of the flow, and digestion does not destroy them all: about half is left as 35,000 tDS of cake, which is spread on farmland. What leaves in a storm-overflow discharge bypasses treatment altogether and is in none of these figures.
• From that sludge it generated 35.2 GWh of electricity, exported 40.3 GWh of biomethane to the gas grid and made 66.3 GWh of heat, of which 27.5 GWh was not used. Source
• It generates 23% of its own energy needs (2024-25). Its target was 35%. Source
• Its sludge energy earned £6.6m of renewable-energy subsidies in 2025-26. Source
• Bathing waters: 78 of 112 classed Excellent in 2025 (75 of 110 in 2024). Source

What we think is still being wasted

• Heat. 27.5 GWh of heat from sludge digestion went unused. What could use it?
• Renewable schemes that did not get built. Welsh Water says some were held up by "planning approval and third-party land issues". Which, and where?
• Farm and food waste. Welsh Water already tankers sludge about three times more watery than slurry to a few digesters; could farms that are too small for their own send theirs the same way, and take the cake back? It states about 7,053 tDS a year of spare capacity at its digestion plants. A farm-scale slurry digester is a different business: roughly 25–40 kWe for the slurry of 250 housed cows, costing £200,000–£500,000 (an estimate and a sourced range; see the working). Per 100 farm digesters we estimate 10–60 jobs would be permanent: real, but nothing like the thousands the first version claimed.
• Heat on dairy farms. One dairy farm in south-west England reports saving about £70,000 a year, paying back in 2 years or less, by taking the heat out of its fresh milk to heat its washing water (the Guardian, September 2026). That is one farm's own figures, as reported; but it is the kind of small, measurable win that waste-as-a-resource should be about. Is there an equivalent in Wales?
• Who pays. Ofwat accepted a £44.72m package from Welsh Water in June 2026, "entirely funded by the company, rather than customers". Welsh Water has no shareholders. Where does the money come from?

These are the questions we think should be asked, with the evidence for each.

Where the numbers come from

Every number on this site is on Sources and estimates, marked as sourced, live or estimate, with the source link or, for an estimate, how we got it and how sure we are. If you find one that is wrong, please tell us.