Interpretation of Results

In order to determine whether a bathing water has met the European Commission (EC) Bathing Water Directive's standards for bathing water quality at least 20 samples have to be considered.

EC Bathing Water Directive's requirements for monitoring programmes

The Annex to the EC Bathing Water Directive contains information on the requirements for monitoring programmes, lists the 19 parameters and values which apply to bathing waters and states how results should be interpreted. The information in the Directive has been transposed to Northern Ireland legislation in the form of The Quality of Bathing Water Regulations (Northern Ireland) 1993.

The Directive contains information on the two main types of values for water quality standards: mandatory standards, which Member States must observe, and stricter guideline standards, which Member States should also endeavour to observe. It is also worth noting that all waters, which comply with the stricter guideline standards also, achieved a pass of the mandatory standards.

Mandatory standards

Mandatory standards apply to 10 parameters; total coliforms, faecal coliforms, salmonella, enteroviruses, pH, colour, transparency, surface-active substances, mineral oils and phenols.

The EC bases compliance with the directive's mandatory standards on the counts of the total coliforms and faecal coliforms. Both parameters must comply with the directive's mandatory standards for the site to achieve a pass at this level.

Guideline standards

In addition to the mandatory standards set by the directive, there are guideline standards of the parameters including the two coliform groups and faecal streptococci. These guideline standards are stricter than the mandatory standards and if achieved, indicate excellent bathing water quality.

The EC bases compliance with the directive's guideline standards on the counts of total and faecal coliforms. Both parameters must comply with the directive's guideline standards for the site to achieve a pass at this level. The UK Government bases compliance with the directive's guideline standards on the counts of total and faecal coliforms and faecal streptococci.

Deviations from these standards are allowed in the case of floods, other natural disasters and abnormal weather conditions under Article 5.2 of the EC Bathing Water Directive

Sampling Frequency

The minimum frequency of sampling is also set out in the Annex to the directive. Checks must be made for the total and faecal coliforms, transparency, colour, mineral oil, surface-active substances and phenols at least once a fortnight during the bathing water season. For the remaining parameters concentrations should be checked wherever inspections show that these substances may be present or where quality of the bathing water has deteriorated.

The bathing season in Northern Ireland is taken from 1 June to mid September.

Interpretation of Microbial Values

The microbiological parameters listed in the directive are all natural inhabitants of the gut of humans and other warm-blooded animals, and are all indicators of sewage pollution. Their presence, in excess of the values in the directive, identifies waters which have almost certainly received volumes of sewage that have not received the treatment or the dilution normally considered necessary (agricultural run-off may also be the cause of the presence of these microbial indicators). The bacteria and viruses present in sewage may cause illness, especially as a result of ingestion or infection through cuts or wounds. Article 5 of the directive specifies how the results of faecal coliform and faecal streptococci monitoring are to be interpreted. These are summarised in the table below. Details of the results obtained from 20 samples are provided, as this is the minimum number of samples which is required to be taken from each identified bathing water in Northern Ireland during the bathing season.

If you have any questions on bathing water quality in Northern Ireland please email EP@doeni.gov.uk