Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/1040774
Databank www.wwtonline.co.uk | WWT | NOVEMBER 2018 | 23 GOAL 3 DRINKING WATER QUALITY I mproving drinking water in AMP7 is no easy task, with 99.96 per cent of the supplies tested in 2017 compliant with the EU Drinking Water Directive – a € gure that has remained largely unchanged since 2004. Instead of concentrating on this € gure, Ofwat has chal- lenged companies to improve their scores according to the Compliance Risk Index (CRI), which was introduced by the Drinking Water Inspectorate (DWI) in 2016 to provide a numerical value that re‹ ects the risk arising from treated water compliance failures. Designed to be proportional across companies, it assigns a value to the signi€ cance of the failing parameter, the propor- tion of consumers potentially aŒ ected and an assessment of the company response. The DWI has also introduced the Event Risk Index (ERI), which has been designed to illustrate the risk arising from drinking water quality events. In simple terms, while CRI indi- cates the risk that a water quality event will occur, ERI indicates the potential consequences of such an event when it does occur. Companies are seeking to mini- mise risk overall, so companies are attempting to keep both CRI and ERI scores as low as pos- sible, with zero representing an ideal score where risk has been eliminated altogether. The € rst year of these measures has seen early signs of improvement: the average CRI score for companies in England and Wales dropped to 3.56 in 2017 from 4.78 a year earlier. Coliforms at treatment works and reservoirs were responsible for 45 per cent of the total value this time around, with the CRI score re‹ ecting their potential to aŒ ect large numbers of customers. The ERI score for all companies in England and Wales in 2017 was 249, also a signi€ cant improve- ment on the retrospectively calculated 346 for 2016. Overall, there were 504 wa- ter quality events in 2017, barely changed from the 505 the previ- ous year, with 228 classi€ ed as 'signi€ cant' and 10 as 'serious'. DRINKING WATER QUALITY Minor Signifi cant Serious Air in water 3 1 0 Chemical 10 7 0 Discoloured water 19 61 1 Inadequate treatment 6 29 2 Loss of supplies/poor pressure 37 28 1 Microbiological 40 31 4 Taste/odour 46 9 0 Health concern 1 4 0 Public concern 83 32 1 Other 10 14 1 TOTAL 255 216 10 Ordered by CRI (lower numbers represent lowest risk) CRI ERI Portsmouth Water 0.01 561.995 Bristol Water 0.03 7.909 SES Water 0.23 0.052 Wessex Water 0.52 13.720 Thames Water 1.22 478.223 Cambridge Water 1.28 0.070 United Utilities 1.28 295.073 South West Water 1.54 6.183 Essex & Suff olk Water 1.60 460.740 South East Water 2.03 69.171 Northumbrian Water 2.79 201.268 Dwr Cymru Welsh Water 2.85 56.042 Anglian Water (inc. Hartlepool Water) 3.17 10.800 Yorkshire Water 4.61 13.857 Southern Water 5.46 1595.305 Affi nity Water 6.66 104.076 South Staff s Water 7.26 47.439 Bournemouth Water 8.71 3.542 Severn Trent Water 9.44 130.279 Dee Valley Water N/A 47.414 Nature of water quality events in England in 2017 Cause of water quality failures for companies based wholly or mainly in England in 2017 (source: DWI) Compliance Risk Index (CRI) and provisional Event Risk Index (ERI) fi gures for 2017 266 Number of 'minor' events occurring in England and Wales in 2017, down from 323 in 2016 4.78 CRI score for companies in England and Wales in 2016 3.56 CRI score for companies in England and Wales in 2017 228 Number of 'signifi cant' events occurring in England and Wales in 2017, up from 174 in 2016 10 Number of 'serious' events occurring in England and Wales in 2017, up from eight in 2016 Public water supply compliance with the EU Drinking Water Directive across England and Wales in 2017, matching the 2016 fi gure (source: DWI) (source: DWI) 99.96% Compliance risk index Coliforms 160 Taste and odour 138 Iron 70 Lead 69 E.coli 38 Pesticides 36 Nickel 30 Manganese 16 Aluminium 13 Benzo(a)pyrene 7 Other 16