| ANH | Heigham WTW | Other – Specify Below: Breach of regulation 31 | 2 | 12,225.087 |
| SST | Hampton Loade – Elevated Geosmin | Treatment failure upstream of final disinfection | 4 | 8,463.380 |
| SST | Hampton Loade Main E – Enterococci | Microbiological Contamination – Treatment works | 3 | 884.591 |
| SRN | Tenants Hill WSR Potential Ingress | Structural failure – Service reservoir | 4 | 600.692 |
| TMS | Ashford WTW Bromate Issue | Treatment failure upstream of final disinfection | 3 | 443.492 |
| TMS | Cryptosporidium detection at Kempton park WTW | Cryptosporidium in Final Water | 3 | 357.440 |
| YKS | Chellow Heights WTW – bacti failure | Microbiological Contamination – Treatment works | 4 | 167.468 |
| SRN | Fairlight Old WSR Ingress | Structural failure – Service reservoir | 4 | 144.261 |
| SRN | Darland Chatham WSR West South Cell ingress | Structural failure – Service reservoir | 4 | 74.582 |
| ANH | Winterton Holmes WTW – Hardness | Other – Specify Below: Water hardness | 3 | 73.694 |
| NES | Wear Valley Network Discolouration | Plant failure – Specify Below: PLC fault causing a shutdown and a faulty valve in the network not closing | 2 | 47.983 |
| SEW | Kippings Cross 1&2 SR ROV Ingress | Structural failure – Service reservoir | 2 | 43.758 |
| YKS | Chellow Heights WTW Operational E. coli | Microbiological Contamination – Treatment works | 4 | 41.435 |
| TMS | Cryptosporidium detection at Dorney Taplow WTW | Cryptosporidium in Final Water | 4 | 40.678 |
| SEW | Polegate/Eastbourne Loss of Supply | Mains problem/ damage – Mains – Burst | 3 | 27.446 |
| AFW | Detection of Enterococci in a Sample from Clay Lane 36″ WTW | Other – Specify Below: Root cause not identified, however the company has not yet completed its investigation (internal inspection of backwash tanks required). | 3 | 25.908 |
| SRN | Yew Hill WSR Enterococci Detection | Structural failure – Service reservoir | 4 | 23.193 |
| SST | Multiple Coliform detections Penkridge Area | Microbiological Contamination – Distribution | 3 | 21.819 |
| TMS | Burst Main – 36” strategic main SE16 | Mains problem/ damage – Mains – Burst | 1 | 21.575 |
| SEW | Sevenoaks Loss of Supplies / Media Interest | Plant failure – Failure – Power | 3 | 21.384 |
| SRN | Easton WSW Nitrate above PCV | Raw water deterioration | 3 | 20.348 |
| ANH | Welton WTW – post UV Enterococci detection | Microbiological Contamination – Treatment works | 4 | 19.031 |
| SWB | Dousland WTW – Loss of Supply | Plant failure – Specify Below: Raw water minas burst following comms failure. | 4 | 17.494 |
| TMS | Restriction of Use (Do Not Drink or Cook) issued to a property in London, EN7 | Planned work – Company staff | 3 | 17.260 |
| NES | Saxmundham discolouration | Planned work – Company staff | 3 | 16.937 |
| WSX | Bourton WTC 2,4-D and MCPA | Ground Contamination / Spillage – Pesticide | 3 | 16.690 |
| AWI | Beaulieu Park E. coli | Other – Specify Below: Failing sample was collected from a hydrant by a non-accredited sampler. Sampling environment was a new housing development, and it is likely the sample was contaminated during collection. | 3 | 15.528 |
| TMS | Cryptosporidium detection at Dorney Taplow WTW | Cryptosporidium in Final Water | 3 | 15.086 |
| SEW | Trosley LOS | Plant failure – Failure – Disinfection System | 2 | 11.356 |
| UUT | Oswestry WTW Power Outage | Plant failure – Failure – Disinfection System | 4 | 11.222 |
| ANH | Stonewall Reservoirs – repeat coliforms |
| 4 | 10.350 |
| SWB | Colyton and Musbury Taste & Odour | Satisfactory investigation, did not identify root cause | 3 | 10.293 |
| SWB | Alderney Cryptosporidium Detection | Deliberate Sabotage | 1 | 10.122 |
| NES | S213 Mill Hill Outlet Discolouration | Emergency Work | 3 | 9.338 |
| SEW | Cottage Hill Discolouration | Planned work – Company staff | 4 | 9.133 |
| SEW | Hawkhurst Discolouration Event | Planned work – Company staff | 3 | 8.760 |
| UUT | Central Manchester discoloured water | Planned work – Company staff | 3 | 8.679 |
| YKS | Embsay WTW enterococcus | Other – Specify Below: No root cause found- investigation not satisfactory | 3 | 8.024 |
| ICW | Welsh Water Outage – Deeside | Mains problem/ damage – Mains – Burst | 3 | 7.536 |
| BRL | Chelvey Raw PFAS Tier 3 detection (Sum of 48) | Raw water deterioration | 4 | 7.277 |
| UUT | Winsford DW | Mains problem/ damage – Mains – Burst | 4 | 7.199 |
| SEW | Malders No.2 SR Ingress | Structural failure – Service reservoir | 4 | 6.052 |
| TMS | Burst 18 inch main in Crystal Palace, London | Mains problem/ damage – Mains – Burst | 3 | 5.981 |
| UUT | Ashworth Moor WTW – Chlorate | Structural failure – Treatment works | 2 | 4.332 |
| ICW | No Water Event | Mains problem/ damage – Mains – Damage by Third Party/Unknown | 1 | 4.134 |
| AWI | Failure to report sample result -ZAWIN037 | Other – Specify Below: Failure to report a regulatory sample result due to miscommunication with analytical provider | 3 | 3.662 |
| SRN | Upper Enham WSR Enterococci Detection | Structural failure – Treatment works | 1 | 3.569 |
| SES | Godstone Air | Planned work – Company staff | 2 | 3.486 |
| YKS | Embsay WTW enterococcus | Other – Specify Below: No root cause found- Investigation not satisfactory | 3 | 3.482 |
| NES | Water Quality Zone T201 Discolouration | Plant failure – Specify Below: Electrical fault on coagulation dosing MCC | 3 | 3.466 |
