What is the CRI? The Compliance Risk Index (CRI) measures overall performance against national drinking water quality standards. A CRI of 0 means all tests passed. A higher CRI indicates more compliance failures relative to the volume of water supplied. Published annually by the Drinking Water Inspectorate (DWI) for England and Wales. Source: DWI Jan–Dec 2024, via DiscoverWater.co.uk (OGL v3.0). E&W average CRI 2024: 3.72.
| Rank (best CRI first) | Company | CRI 2024 | GWSS |
|---|---|---|---|
| #1 | SES Water | 0.00 | 93.2/100 |
| #2 | Portsmouth Water | 0.45 | 88.9/100 |
| #3 | South East Water | 1.09 | 75.8/100 |
| #4 | Hafren Dyfrdwy | 1.10 | 64.2/100 |
| #5 | South West Water | 1.19 | 79.5/100 |
| #6 | Wessex Water | 1.31 | 77.9/100 |
| #7 | Affinity Water | 1.44 | 84/100 |
| #8 | Thames Water | 2.04 | 62.7/100 |
| #9 | Anglian Water | 2.11 | 87.1/100 |
| #10 | Bristol Water | 2.84 | 89.7/100 |
| #11 | Yorkshire Water | 3.61 | 70.8/100 |
| #12 | Southern Water | 3.82 | 50/100 |
| #13 | Dŵr Cymru Welsh Water | 4.18 | 19.4/100 |
| #14 | Cambridge Water | 6.58 | 73.1/100 |
| #15 | South Staffs Water | 6.58 | 64.3/100 |
| #16 | United Utilities | 10.28 | 48.2/100 |
| #17 | Severn Trent Water | 10.32 | 58.2/100 |
| #18 | Essex and Suffolk Water | 10.94 | 69.4/100 |
| #19 | Northumbrian Water | 10.94 | 58/100 |
Source: Drinking Water Inspectorate (DWI), accessed via DiscoverWater.co.uk (CSV: 2025-CRI-Current-UK.csv, 2025-CRI-Previous-UK_2025-12-17.csv). CRI = Compliance Risk Index. Lower = better quality compliance. Open Government Licence v3.0. GWSS methodology. Note: some companies are reported in groups (e.g. Northumbrian and Essex & Suffolk) — both receive the same CRI.