Corrected 2 October 2026 · version 2.0.0. The first version of this site made claims that were wrong. What changed and why · the original, kept
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Figures by topic

The same figures as Sources & estimates, grouped by topic.

Sludge: what Welsh Water reports

Share of sludge treated by advanced anaerobic digestion

98.2%2025-26sourcedhigh confidence

The company's reported result for the year, not a target. A company-wide share of all sludge, by weight; the target in its price review was 97.3% (the 2024-25 result was 98.3% on that measure, and it says 'a small volume' was not processed through the four plants because of maintenance). A further 0.2% went through advanced digestion run by a third party. Most sludge is made elsewhere and carried to the four plants; our check of its routing data is below.

Welsh Water, Annual Performance Report 2025-26 (tables)Table 8D, line 8D.4, 'by incumbent'

Share of sludge made at the four works that have an advanced digester on site

37.3%2024-25sourcedmedium confidence

This is why 98% of the company's sludge can be digested although it has hundreds of works: the 98% is company-wide, not per site. Our sum from the company's published return, not a figure the company states.

Welsh Water, Bioresources market information 2024-25sheets WwTW, Small WwTW and STC: sludge made at the works co-located with Afan, Cardiff Bay, Cog Moors and Five Fords, as a share of all sludge listed

2,432.165 + 13,966.739 + 7,151.686 + 4,613.634 = 28,164.224 tDS, of 73,932.593 tDS from the 137 larger works plus 1,493.447 tDS from the 450 small works (75,426.039 tDS). The rest, about 63%, is made at other works and carried to a digester, or to a thickening or dewatering centre first, by tanker or pipeline.

Share of sludge we can trace, through the company's published routes, to an advanced digester

90.9%2024-25sourcedmedium confidence

An independent check on the reported 98%, and a floor, not an estimate of the whole. It shows the 98% is an outcome of where the tonnes actually go, not a target. Our arithmetic from the company's published return.

Welsh Water, Bioresources market information 2024-25sheets WwTW, Small WwTW and STC: where each works sends its sludge, and where each treatment centre sends it on

Each of the 137 larger works names where its sludge goes (and what share). Each of the 23 thickening and dewatering centres, and the two conventional digesters, names where they send it on, and almost all of it goes to Afan, Cardiff Bay, Cog Moors or Five Fords. Following the tonnes through those links puts 68,591 of 75,426 tDS at an advanced plant. The other 9% cannot be traced in the return: the 450 small works give no route (1,493 tDS), some routes do not add up to 100%, and a few destinations are not listed.

Average dry solids of the raw sludge Welsh Water's larger works produce

3.1%2024-25sourcedmedium confidence

Welsh Water already pumps and tankers sludge this watery between its works. Our sum from the company's published return.

Welsh Water, Bioresources market information 2024-25sheet WwTW: quantity of raw sludge and its average dry solids, for the 137 larger works

73,933 tDS of sludge, at each works' own dry-solids percentage, is 2,353,826 tonnes of wet sludge as produced: 73,933 ÷ 2,353,826 = 3.1%. Median works 3.7%; range 0.4% to 7.2%.

Energy from sludge

Rough ceiling on the gas energy in Welsh sludge

190 GWh2025-26estimatelow confidence

Welsh Water reports 141.8 GWh generated from sludge, so most of any ceiling is already being recovered.

70,500 tDS × 450 m³ biogas per tDS × 60% methane × 10 kWh per m³ methane = 190 GWh. The yield, methane share and energy content are typical industry values (the first version of our model used them), not Welsh Water's own. 450 m³/tDS is probably at the high end.

Cost

Storm overflows: the plan

Overflows discharging at any one moment in 2024, on average

96 overflows2024 calendar yearestimatemedium confidence

This is the rate behind the counter on the home page, which adds up discharge time as you read, at the 2024 average.

844,375 site-hours of discharge in Welsh Water's 2024 return ÷ 8,784 hours in 2024 = 96.1. Discharges bunch up in wet weather, so at most hours the real number is far lower and in a storm far higher: it is an average, not a reading. The live count of overflows operating now is on the home page.

The Ofwat packages

Bathing waters

Another company's claims

Bills

Off the gas grid

Wales today

Farm digestion: scale and jobs

Electricity from the slurry of 250 cows housed all year

25–40 kWe2015-2024 sourcesestimatemedium confidence

Our first model assumed 200 kWe for a 250-cow unit. The Farmers Weekly figure it borrowed (275 kWe) was for 250 cows plus 150 hectares of maize, at 2012 prices.

IEA Bioenergy Task 37, Small-scale anaerobic digestion (2015)page 3 of the brochure; and the Farmers Weekly article of 23 October 2024

IEA Bioenergy (2015): 'a typical livestock farm of 100 dairy cows only has an electricity generating capacity of approximately 10 kWe', so about 25 kWe for 250 cows. Farmers Weekly (2024): a 44 kW plant 'should supply enough electricity for a 300-cow indoor dairy unit', about 37 kW for 250 cows. We give 25-40 kWe. It is less if the cows are housed only part of the year.

Permanent jobs per 100 farm digesters of 200 kWe

10–60 jobs2012 coefficientsestimatelow confidence

Our first model counted about 35 per 100 as well, but for 1,125 plants of a size and number that cannot be supported.

NNFCC for DECC, UK jobs in the bioenergy sectors by 2020 (April 2012)Figure 19: 0.21 design, 1.18 construction, 2.21 permanent and 0.14 contract operation, 0.50 feedstock (FTE per MWe)

NNFCC's coefficients: operation 2.21 permanent + 0.14 contract, and feedstock 0.50, full-time equivalents per MWe installed. 100 plants of 0.2 MWe is 20 MWe: (2.21 + 0.14 + 0.50) × 20 = 57 jobs. At the low end, only contract maintenance counts, because the farmer runs the plant: NNFCC assumes one contract worker per 10 plants, so 10. NNFCC's sample averaged plants of about 1.2 MWe, so scaling down probably overstates. A slurry-only plant of 25-40 kWe would employ far fewer.

Slurry from roughly this many dairy cows would fill Welsh Water's stated spare digester capacity

2,000–4,500 cows2024-25estimatelow confidence

A pilot, not a solution, unless capacity is built. Welsh Water does not say it would accept farm slurry.

7,053 tDS of spare capacity ÷ 9% dry matter = about 78,000 tonnes of slurry a year; ÷ 23 tonnes a cow a year = about 3,400 cows housed all year. That is roughly 1.3% of Wales' 254,100 dairy cows. Capacity for a watery feedstock is often limited by volume, not only dry solids, so this may overstate it; cows housed for part of the year make less slurry, so it may understate the herd. Hence the wide range.

Saving a year at Barber's Farmhouse Cheesemakers from milk-source heat pumps in three of its seven milking parlours

£70,0002024-26sourcedmedium confidence

The farm and the heat-pump supplier, Arkaya Energy, as reported by a journalist. We have not seen the data. One farm in south-west England, not Wales.

The heat pumps cool the milk and use the heat taken out of it to heat washing water to 92°C. The farm says they halve its electricity use.

The Guardian (from Canary Media), 'It bloody works': why the world's oldest cheddar-maker uses a 'milk-source' heat pump, 17 September 2026'saving Barber's about £70,000 a year'

Live data