The concentration or value is expressed in different units. Most of the parameters sampled are in milligrams per litre (mg/l) or micrograms per litre (µg/l). These are very small amounts. One mg/l is one part in 1,000,000 parts of water (or 0.0001%). One µg/l is one part in 1,000,000,000 parts of water (or 0.0000001%)

These standards are set down in the Water Supply (Water Quality) Regulations 2000 in line with European (EC) requirements. They are the acceptable levels of certain elements, compounds or substances which are allowed in drinking water. Usually this is a maximum allowed level but occasionally it can be a minimum allowed level.

This is the number of samples collected from the zone during a period of time, usually the previous 12 months.

This is the number of samples that has breached a parameter limit or PCV.

This column shows the percentage of results, which failed the standard for each parameter sampled. This is expressed as a percentage of the total number of samples for that parameter. For example, 2% shows that 1 sample in 50 failed. In most cases, you will see a value of 0, which demonstrates that the water has met the standard every time a sample was collected.

This demonstrates a summary of the results from the tests over the time period. The minimum, mean and maximum concentrations are shown. The < symbol shows that the value recorded was below measurable limits. The mean is calculated by adding up all the results and dividing it by the total number of tests for that parameter.