Water Quality Standards
Drinking water standards in the United Kingdom are some of the toughest in the world. Here at Severn Trent Water, we strive to make sure that the water is not only safe to drink, but looks and tastes good as well.
The European Union have recently issued revised quality standards relating to drinking water. These, along with some stricter national standards, have been adopted and written into national law in The Water Supply (Water Quality) (England) Regulations 2000. These regulations became effective on 1st January 2004.
who ensures the standards are met?
The primary responsibility for enforcing the standards and Regulations lies with the Drinking Water Inspectorate (DWI). They independently assess the performance of every Water Company and report annually. Local authorities also have some responsibility for checking drinking water quality through their Environmental Health teams.
what do the standards cover?
They cover chemicals, micro-organisms and aesthetic qualities such as colour, clarity and taste. The Water Supply (Water Quality) (England) Regulations 2000 have a fundamental difference from the previous Regulations. They make a distinction between those parameters which are considered to be important to health (mandatory) and others which largely affect the appearance and taste/smell of water (non-mandatory or indicator).
The Regulations also specify the frequency of monitoring for the different parameters. Check monitoring requires frequent monitoring for microbiological parameters and those chemical parameters that may be affected by treatment processes. Audit monitoring is less frequent.
how are the standards set?
The standards, which are called ‘Prescribed Concentrations or Values’ (PCVs) are set in a variety of ways. Most define maximum and a few minimum levels, while some state the percentage of samples which must meet the required standard.
what units of measurement are used?
The units are extremely small, for example:
- 1 milligramme per litre (mg/l)
is 1 part in 1,000,000 (million) - 1 microgramme per litre (ug/l)
is 1 part in 1,000,000,000 (billion) - 1 nanogramme per litre (ng/l)
is 1 part in 1,000,000,000,000 (trillion)
Many of the measurements are very near the limits of detection, even with the most sophisticated instruments. For example, the individual pesticides standard (one part in ten billion) is almost twice as difficult to detect as looking for one person in the whole world’s population.
must the standards be met?
Yes and Severn Trent Water is committed to ensuring that you receive drinking water that is both dependable and of high quality.
what happens if a standard is not met?
Any exceedance of a standard is always immediately investigated and remedial action taken. In the vast majority of cases such exceedances are minor and temporary in nature. However, all must be reported to the DWI, who can further investigate if they choose. In the rare circumstances that an exceedance of a standard cannot be rectified promptly, then the DWI can require us to take further action.
Provided there is no risk to health, these actions are written into a legally binding commitment to implement programmes stating how and when we intend to achieve compliance.
Our standards are amongst the highest in the UK. In fact, less than 0.1% of all samples taken do not meet the standards. This has been a consistent trend and it is a record we are proud to maintain.