Bathing Water Quality
On this page: Classifications | Water Quality Assessments | Abnormal Situations | Pollution Risk Forecasting | Short term pollution
The Environment Agency takes up to twenty water samples at each of England’s designated bathing waters during the bathing water season between May and September each year. A classification for each bathing water is calculated annually based on samples from the previous four years. These classifications are:
- Excellent – the highest, cleanest water quality
- Good – generally good water quality
- Sufficient – the water meets the minimum standard
- Poor – the water has not met the minimum standard. Work to improve quality at Poor sites are detailed in the site’s profile.
If a bathing water is classified as Poor, then a sign advising against bathing will be displayed. However, the beach remains open for people to enjoy.
The use of standardised symbols for the four classes helps people make informed choices on where to swim.
A sample tells us the quality of the water at that specific time, but water can change even over the course of one day. In each sample we test for bacteria that indicate whether there is faecal matter in the water. These bacteria are known as faecal indicator organisms or FIOs and the specific ones that we test for are:
- Escherichia coli or E. coli (EC)
- Intestinal enterococci (IE)
These bacteria can come from many sources including sewage, agricultural livestock, wildlife, birds and road drainage.
When more of these FIOs are present in a bathing water they can indicate greater risks to a bathers' health. The standards we use for levels of FIOs are specified in the Bathing Water Regulations and are based on World Health Organisation research which recorded the frequency of stomach upsets in people bathing in differing water quality.
The annual classification uses the samples taken over four years to build an assessment of typical water quality and is a good way to compare bathing water locations.
Water Quality Assessments
Designated bathing waters in England have tough water quality targets to achieve. Concentrations of Escherichia coli (EC) and Intestinal enterococci (IE) are used to classify a bathing water. The classifications are based on the analysis of samples taken over a four year period. If a step change in quality has occurred because of an improvement action such as new sewerage infrastructure, only data collected since the action will be assessed.
There are no pass/fail standards for individual water samples, instead the classification is based on a statistical measure of all samples, known as a percentile. Percentiles use the range of all samples taken to estimate the probability of higher results occurring. The classification uses either the 95% or 90% percentile depending on the classification.
The criteria for coastal bathing waters and inland bathing waters are different. The thresholds for classifications are as follows:
|Coastal Bathing Waters|
|Excellent||EC: ≤250 cfu/100ml ; IE: ≤100 cfu/100ml (95th percentile)|
|Good||EC: ≤500 cfu/100ml ; IE: ≤200 cfu/100ml (95th percentile)|
|Sufficient||EC: ≤500 cfu/100ml ; IE: ≤185 cfu/100ml (90th percentile)|
|Poor||means that the values are worse than the sufficient|
|Inland Bathing Waters|
|Excellent||EC: ≤500 cfu/100ml ; IE: ≤200 cfu/100ml (95th percentile)|
|Good||EC: ≤1000 cfu/100ml ; IE: ≤400 cfu/100ml (95th percentile)|
|Sufficient||EC: ≤900 cfu/100ml ; IE: ≤330 cfu/100ml (90th percentile)|
|Poor||means that the values are worse than the sufficient|
If water is classified as Poor, then the symbol for "poor" together with a sign showing advice against bathing must be displayed in the following year. A sign displaying a "poor" classification and advice against bathing does not mean bathing is banned or that a beach is closed, beaches remain open for people to enjoy.
If a pollution incident occurs that may affect water quality, we will issue advice against bathing and may suspend routine monitoring until the incident is over. On occasions, samples will be taken during conditions (such as extreme rainfall) that are later found to be abnormal and may be disregarded from classification.
These situations are defined in the Regulations as an abnormal situation where this type of pollution is not likely to occur more than once in four years on average. Disregarding samples in this way means the classification assessment will be representative of normal conditions that bathers are likely to encounter.
Pollution Risk Forecasting
At some bathing waters we are able to let bathers know that on some days, water quality can be temporarily reduced. This is due to a number of factors which influence the levels of bacteria, or FIOs, in the water. We use Pollution Risk Forecasts (PRFs) to let people know when this happens. The factors that we use for PRFs are specific to each bathing water and include:
- Rainfall - this washes FIOs from the land into a river or stream that then flows into a bathing water. The amount and intensity of rainfall are important predictive factors used for PRF along with how long it takes the FIOs from the land to arrive at a bathing water.
- Tides - move any FIOs, entering the sea both from rivers or streams, both towards and away from bathing waters twice a day.
- Wind - can blow and move any FIOs at the surface of the water but also disturb FIOs stored in beach sediment through wave action.
- Sunlight - kills FIOs in the water through ultraviolet rays. So bright days increase this effect, but cloud and silt in the water can prevent this.
- Seasonality is an important factor in predicting the number of FIOs in the water. The reasons behind this may include day length, water temperature, number of bathers in the water and changes in use of the sewerage infrastructure.
Pollution risk forecasts look at trends in past data to predict average water quality. If the average quality is forecast to be above a warning threshold, then a pollution risk warning is issued for the day. This enables bathers to avoid times or locations where the risk of temporary pollution is higher.
Not all bathing water locations are suitable for PRF. The water quality at some bathing waters is of a very high standard all the time and others are affected by pollution sources that are too complex or can’t be measured by our system - these could include factors such as seagull numbers, or even the number of bathers themselves.
At the moment PRFs don’t directly use permitted discharges from the sewerage infrastructure to make forecasts of water quality. In most cases ‘spills’ from the storm overflow network will be associated with heavy rain, so often when a spill occurs a warning will have been issued because of the rainfall. It’s hoped that integration of the sewerage system’s telemetry data into PRFs may be possible, but this would require future work with the water industry to assess criteria to decide which spills are likely to be significant for each bathing water.
Short term pollution
Short Term Pollution is pollution that has clear causes, can be predicted and is expected to affect the quality of a bathing water for less than 72 hours. We use Pollution Risk Forecasting to let people know when this will happen.
At the bathing waters where PRF is possible, there is an agreement with local authorities for them to display warning signs at a bathing water when a pollution risk warning is issued. If one of these warnings is seen to be in place by our samplers when taking a sample and meets relevant criteria, then the sample may be disregarded from the set which is used to make the annual classification. This is done under the ‘Short Term Pollution’ provisions of the Regulations. This provision means that the classification reflects the water quality when advice against bathing wasn’t issued, and when people are likely to be using the water.
The samples disregarded under the Short Term Pollution provisions are however taken account of and used to help plan appropriate pollution-prevention measures to further protect bathers.
These water quality warnings are shown on the main map on the home page, profile pages for individual bathing waters, and the compare bathing waters page. They are indicated by a warning circle icon .
Up to 15% of samples used in the
classification data may be removed over the four year period. This discounting
assessment is made at the end of each monitoring season and is shown in the data