Each individual company section contains the following where appropriate:

• A general statement about overall water quality in 2003
  
• Company Information
  
• Water quality in water supply zones, at treatment works, and in service reservoirs
  
• Company audit and inspection
  
• Incidents
  
• Prosecutions (if any)
  
• Improvement programmes carried out by the company
  
• Enforcement action
  

Comparison of water quality

The information given in the sections about water quality in each company's area indicates the extent to which the company has, or has not, complied with the requirements of the Water Supply (Water Quality) Regulations 1989 (the Regulations). It should not be used simplistically to make comparisons of the overall quality of drinking water between different company areas or of the relative efficiency of different companies.

The quality of drinking water varies within and between company areas, and depends not only on the treatment processes employed and the condition of the distribution system, but also on the nature of the source from which the water is obtained. For example, water from a borehole in a chalk aquifer would normally be of better microbiological quality, than water from many other types of source. In addition, it should be noted that for all parameters, the greater the number of samples taken, the more likely it is that breaches of the standards will be detected.

This is not to say that meaningful comparisons of water company performance cannot be made. The Inspectorate has developed statistical procedures for categorising water companies on the basis of quality of water supplied, and on efficiency of managing treatment and distribution, and results obtained using these procedures are presented in Part 1 of this Report.

Microbiological water quality

The detection of coliforms in a sample does not mean that it is likely that the water supply will cause illness, but is indicative of potential contamination that must be investigated immediately. The Regulations require 100 per cent compliance with water quality standards for total and faecal coliforms at water treatment works, and for faecal coliforms at service reservoirs and in zones. They allow no more than five per cent of samples taken in any year from service reservoirs or in zones to contain total coliforms in order to achieve compliance. Breaches may result in enforcement action unless the company has taken remedial action to prevent recurrence.

Breach of standards

Reference to parameters that breached the standards in one or more samples does not mean that any of these breaches resulted in harm to the health of consumers. Only some of the parameters are of health significance and their standards are generally set with a wide margin of safety. The other parameters are of aesthetic significance, with standards set generally well below the level at which water would become unacceptable to consumers, and the breaching of those standards does not mean that the water is unfit to drink.

However, a breach of a standard, even for only one parameter, and in only one sample out of the large number taken from each water supply zone in the course of the year, is of significance because the water supplied at the time the sample was taken cannot be regarded as wholesome. When considered in the light of other results of monitoring, it may mean that some action is required in order to meet the high standards specified in the Regulations.

Consideration of enforcement action

For 2003, the Inspectorate has generally regarded a breach of a standard for an individual (nonmicrobiological) parameter on a single occasion in a water supply zone as trivial, provided that ten or more samples have been taken in that zone, or if a smaller number has been taken, provided that there was not a corresponding breach in 2002. In other cases, the Inspectorate has taken into account the number of determinations carried out and the number and the extent of the breaches, in deciding whether the breaches were trivial or not.

The Inspectorate considers enforcement in all cases where the breaches are not regarded as trivial, unless the company has already taken remedial action to prevent a breach recurring or the Inspectorate judges that the breach is in any case unlikely to recur. A breach of the coliform standard at a consumer's tap is also regarded as trivial if the company can demonstrate beyond reasonable doubt that the breach arose solely as a result of the condition of the consumer's plumbing or tap from which samples were taken.

Quality standards table and glossary

As an aid to understanding the company sections, definitions for all the individual parameters and many of the scientific terms used can be found in the following Quality Standards Table, or in the Glossary in the Annexes of this Report. These definitions apply to current Regulations. From 1 January 2004, the Water Supply (Water Quality) Regulations 2000 and the Water Supply (Water Quality) Regulations 2001 in Wales (the new Regulations) came into force. These Regulations require water companies to monitor against new and revised standards. For further details on the changes to be introduced under the new Regulations, see Chapter J, ‘New Regulations and Associated Programme of Work’, in Part 3