Monitoring requirements and quality assessment methodology

According to the EEA Report No 9/2016 (European bathing water quality in 2015)

The monitoring requirements are:

  • taking of a pre-season sample (taken shortly before the start of the bathing season);
  • a minimum of four samples per season (three samples are sufficient if the season does not exceed eight weeks or if the region is subject to special geographical constraints);
  • a minimum of one sample per month (if, for any reason, it is not possible to take the sample at the scheduled date, a delay of four extra days is allowed. Thus, the interval between two samples should not exceed 31 + 4 days).

These conditions must be met for all reported bathing water sites. If these rules are satisfied, the bathing water is categorised as sampling frequency satisfied. If at least one monitoring requirement is not fulfilled the bathing water is categorised as sampling frequency not satisfied.

If the sampling frequency of bathing water has not been satisfied, it can still be quality assessed if at least four samples per season (three samples if the season does not exceed eight weeks or the region is subject to special geographical constraints) are available and are more or less equally distributed throughout the season, and if the bathing-water sample dataset contains an adequate amount (16 or 12, respectively) of samples.

Bathing water sites are accordingly classified in one of the bathing-water quality classes (excellent, good, sufficient or poor).


Quality assessment is not possible for all bathing water sites. In these cases, they are instead classified as either:

  • not enough samples: not enough samples have been provided for the season of the reporting period or throughout the whole assessment period.
  • new: classification not yet possible because bathing water is newly identified and a complete set of samples is not yet available.
  • changes: classification is not yet possible after changes affecting bathing water quality have been implemented.
  • closed: bathing water is closed temporarily or throughout the bathing season.