e-Digest Statistics about: Inland Water Quality and Use
Water abstractions and supply
Drinking water quality
Water undertakers in the UK are required to supply wholesome water and they are responsible for assessing the quality of the water they supply. New water supply regulations covering all of the countries within the UK, came into force at the end of 2003.
Assessments are done through regular sampling both of the water leaving water treatment works and in service reservoirs for microbiological parameters and at consumers taps in discrete water supply zones in which not more than 100,000 people reside (previously 50,000) for a more extensive set of parameters. In England and Wales, the Drinking Water Inspectorate audits water companies to check whether they comply with the regulatory requirements. In Scotland, the Drinking Water Quality Regulator in the Scottish Executive and in Northern Ireland, the Drinking Water Inspectorate (for Northern Ireland) regulate and assess drinking water quality. In the UK, local authorities check the quality of private water supplies and may also check the quality of public water supplies within their areas.
Table 28 shows that the overall number of tests was less from 2004 onwards due to the redefinition of water company supply zones. The different monitoring requirements of the new regulations mean that data from 2004 onwards is not directly comparable to previous years.
A feature of the Regulations is the introduction of European Union (EU), National (N) and Indicator parameters. Only European Union and National parameters have a prescribed concentration value (PCV). Indicator parameters have no PCV, but exceedances of the specification concentration value triggers investigation. Figures listed in these tables are tests of EU and national parameters only, as these are mandatory parameters, and the closest for comparison with previous years’ data. In the United Kingdom 99.9 per cent of determinations in 2005 complied with the relevant standards and thus, overall, water undertakers complied with the majority of the standards for most or all of the year. The overall compliance rate in England and Wales was just under 100 per cent, in Scotland 99.6 per cent and in Northern Ireland 99.8 per cent.
Table 29, Table 30 and Table 31 give more detailed results for tests taken from the water supply zones in England and Wales [15], Scotland [16], and Northern Ireland [17], respectively. The tables allow comparison of individual parameters up to 2003, although they are not directly comparable to figures after 2003 due to changes in numerical standards from 2004 onwards which includes lead for which a new standard of 25 mg/l applied (previously 50 mg/l). Polycyclic aromatic hydrocarbons (PAH) now relates to the sum of four substances (previously six) whilst trihalomethanes (THMs) now have a tighter standard of an absolute maximum concentration of 100 mg/l (previously three month rolling mean).
The tables cover the available data for 1995 to 2005. They include both numbers and percentages of determinations not complying with the previous regulatory requirements or with the new regulations (2004 data onwards) and also the number and percentage of supply zones not complying under the relevant regulations. In 2005 there were over two million determinations for individual parameters in samples taken from the 1,691 supply zones in England and Wales, over 153,000 samples from 374 supply zones in Scotland, and over 57,000 samples from 69 zones in Northern Ireland.
Overall in 2005, only 0.1 per cent of the determinations from supply zones in the UK contravened the relevant standards. Some of these contraventions are regarded as trivial because this result was not repeated in follow-up sampling and others are regarded as unlikely to recur because appropriate remedial action had been taken. For some parameters non-compliance of a single determination does not mean that the supply zone is in breach of regulations.
Under the new regulations total coliforms are renamed coliform bacteria and faecal coliforms are renamed E.coli. The number of zones failing for coliform bacteria from 2004 onwards is not comparable with previous data. In previous years, zones were only deemed to have failed for this parameter if more than five per cent or more of determinations in the preceding 12 months exceeded the standard. From 2004 this 95 per cent rate applies only to water leaving a service reservoir and by the time it leaves a water treatment works prior to public supply it must not contain any coliform bacteria. For other parameters the zone only fails to comply if the average concentration over the corresponding period exceeds the prescribed concentration.
While the summary statistics for Scotland (Table 30) and Northern Ireland (Table 31) are given in a similar form to those for England and Wales, the patterns across supply zones may not be comparable to those in England and Wales because of the large proportion of very small zones in Scotland and Northern Ireland. Nearly 59 per cent of all Scottish zones serve less than 5000 people and a combined total of about 4 per cent of the total population of Scotland.
Regional data
We do not have data at a lower geographical level. For further information contact the Drinking Water Inspectorate and their annual report.
In Detail:
Further Information:
- Key Facts:
- Drinking water quality
Data Tables:
- References, further reading and links to other resources:
- [15] Drinking Water 2004: A Report by the Chief Inspector, Drinking Water Inspectorate
- [16] Drinking Water Quality in Scotland 2005. The Scottish Executive
- [17] Northern Ireland Drinking Water Quality 2005: A Report by the Northern Ireland Drinking Water Inspectorate, (PDF download)
- Internet Links:
- For national and local information see:
- England and Wales: Environment Agency, Drinking Water Inspectorate
- Scotland: Scottish Environment Protection Agency
- Northern Ireland: Drinking Water Inspectorate, Department of the Environment in Northern Ireland
- Regulations made under the 1998 EC Directive on the quality of water intended for human consumption (98/83/EC)
- England - Water Supply (Water Quality) Regulations 2000
- Wales - Water Supply (Water Quality) Regulations 2001
- Scotland - Water Supply (Water Quality) (Scotland) Regulations 2001
- Northern Ireland - Water Supply (Water Quality) Regulations (Northern Ireland) 2002
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Page last modified: 14 March 2007
Page published: 16 February 2006