Glossary of bathing water quality terms

1976 Bathing Water Directive
This directive was introduced in 1976 to protect and improve bathing water quality, with the aim of protecting human health and facilitating recreational use of natural waters. It was replaced by the 2006 Bathing Waters Directive, replacing the old three-tier classification scheme with a tighter four-tier scheme.
Abnormal situation
An event or combination of events impacting on bathing water quality which the Environment Agency would not expect to occur, on average, more than once every four years. During an abnormal situation water quality monitoring is suspended until the incident is over.
Algae (seaweed and phytoplankton)
Algae are types of plant which can be very small like pinpoints floating in the sea or larger like seaweed growing on the sea bed.
Bathing water quality
How clean a bathing water is.
Bathing water sample point
The point at a bathing water where we take water samples. This is at the place where most bathers are expected.
Bathing water season
The bathing water season in England runs from 15 May to 30 September when we expect the most people at bathing waters. Water quality is regularly checked during the season.
Bathing Water Directive
The (revised) Bathing Water Directive (2006/7/EC) was fully implemented on 24 March 2015. The revised directive standards are much stricter than those for the old Directive.
Bathing Waters Directive classification
There are four classifications of water quality:
  • "excellent" – the highest, cleanest class
  • "good" – generally good water quality
  • "sufficient" – the water meets minimum standards
  • "poor" – the water has not met the new minimum standards. Work is planned to improve bathing waters not yet reaching sufficient.
Blue Flag
More information can be found here:
Body of water
A volume of water, such as part of a river, lake, stream or the sea.
The catchment of a bathing water is the surrounding area of land where water drains into that bathing water
Coastal bathing waters
There are two types of bathing waters – coastal and inland. The directive has different standards for these types of waters.
Colony Forming Units (cfu)
This is an estimate of the number of bacteria in a sample of water. This is done by counting the number of colonies (groups) of bacteria growing on a filter through which the sample has been passed.
Competent authority
The organisation that has responsibility for monitoring and protecting a designated bathing water. In England this is the Environment Agency, in Scotland the Scottish Environmental Protection Agency, in Wales, Natural Resources Wales and in Northern Ireland, the Department of Environment Northern Ireland
Compliance with the Bathing Water Directive
Each year, every bathing water receives a water quality classification. We measure the number of certain types of bacteria, which may indicate the presence of pollution, mainly from sewage or animal faeces. Escherichia coli (E.coli) and Intestinal enterococci (IE) are bacteria that indicate the presence of faeces. An increase in the concentrations of these bacteria indicates a decrease in water quality.
Impurity or pollution.
Combined Storm Sewage Overflow (CSO)
Overflow pipes designed to relieve pressure on sewerage systems during periods of high rainfall, with the aim of preventing sewage from flooding homes. Overflows allow rainwater and diluted sewage (usually screened to remove solids), to bypass sewage treatment works and flow directly into rivers and coastal waters.
CSO Discharge
When a CSO discharges either because of heavy rain or unexpectedly due to an incident such as a blockage or broken pipeline.
A type of bacteria that grow in water and get their energy from the sun, like plants. These sometimes rapidly multiply and form blooms and scums in fresh-water that are sometimes are poisonous
Daily pollution forecast
See Pollution Risk Forecast
Designated bathing water
Designation in England is made by the Department of Environment Food and Rural Affairs (Defra). More information can be found from Bathing waters: apply for designation or de-designation.
Diffuse pollution
Run off from land (urban and rural) across a catchment, which can affect bathing water quality.
Water quality samples taken during a short term pollution event can sometimes be disregarded. A pollution risk warning must have been issued and signs displayed advising against bathing when the sample was taken. Only 15% of samples can be removed from the classification data over a four year period.
Samples taken during a short term pollution event which have been removed from the classification data.
Disused outfall
A pipe that is no longer used to discharge waste water.
DNA tracing technique or MST
Microbial Source Tracking (MST) is when we use DNA tracing to establish whether pollution at a bathing water is from humans, farm animals, birds or other sources.
Liquid waste or sewage discharged into the environment.
Emergency or storm overflow
A pipe in a sewerage system which only discharges during emergencies or when there is heavy rainfall which can cause a risk of flooding in the sewer system.
Escherichia coli (E.coli)

E. coli are a group of organisms found in the intestines of animals and humans and survive for a while in the environment when excreted. Many types of E. coli are not harmful but some such as E. coli 0157, can directly cause illness. The presence of the bacteria indicates that human or animal faeces may be present in bathing water and could contain other potentially harmful organisms that could cause illness.

Occasionally, usually during heavy rainfall, soil containing E. coli bacteria is washed into, rivers, streams, lakes, or groundwater leading to bathing waters, and if found, E. coli bacteria indicates that harmful bugs could be present.

Faecal matter
Animal and bird waste.
Inland bathing waters
There are two types of bathing waters – coastal and inland. The directive has different standards for these types of waters.
In-season measurement
A bathing water sample taken and analysed during the bathing season.
Intestinal Enterococci (IE)
Intestinal Enterococci are found in the intestines of animals and humans although some types are environmental in origin. The presence of the bacteria indicates that human or animal faeces may be present in bathing water alongside other potentially harmful organisms that could cause illness.
Investigations take place to find out the reasons for changes in water quality.
Algae made up of more than one cell, such as seaweed.
Misconnections (also called wrong connections)
Misconnected sewage pipes which go directly into surface water drains are a significant source of pollution. Misconnections can happen when domestic plumbing has been connected into surface water drains instead of the foul sewer. This means untreated dirty water goes directly into the environment. Find out more at ConnectRight.
Each bathing season we take samples at every designated bathing water to monitor their quality. We also take a pre-season sample in early May. These are analysed and the results are posted on the Bathing Water Data explorer.
Not sampled
Indicates that the bathing water was closed during the bathing season, so no samples were taken.
A permit sets the standards or criteria that sewage discharge or outfalls must meet to protect water quality
Tiny plants found in water.
Anything that can reduce water quality, for example, sewage animal or bird faeces.
Pollution incident
Bathing water quality can be affected by pollution which may pose a risk to bathers' health. Information on a pollution incident will be displayed on the bathing water data explorer and at the beach
Pollution risk forecast
Pollution risk forecasts are predictions that use rainfall or other factors to assess when there may or may not be a risk of reduced bathing water quality. We can’t make these forecasts for all bathing waters as not all are at risk from these issues.
The description of a designated bathing water and its catchment.
Sea outfall pipe
A pipe that discharges treated waste water or storm water and sewage.
Waste water from toilets, sinks, showers and washing machines that comes from homes and businesses.
Sewage treatment works outfalls
Where the treated water comes out.
Sluice gate
Valve or gate fitted to a sluice (channel that carries a rapid current of water) to control the rate of flow of water.
Spill frequency
The number of times an overflow discharges.
Step change
Where a significant action has been carried out to improve the bathing water quality. Data is used from the time that the improvement took place to assess compliance, rather than a 4 year set of data.
Surface water outfall
A pipe that discharges rainwater which has fallen on the land and runs into drains and gutters before being discharged.
Surface water runoff
Rainwater that flows off land including, roofs, roads, pathways, driveways, hard standings and car parks.
Ultra Violet (UV) treatment
Ultraviolet light is passed through treated sewage waste to reduce the numbers of micro-organisms.
Water company
Water companies supply water services in England and Wales. Some are water supply only companies and some are combined water and sewerage companies.
Water Quality Assessment
How we calculate how clean bathing water quality is.
Water Framework Directive (WFD)
The European Union legislation Water Framework Directive (2000/60/EC) establishes a framework for European Community action in the field of water policy.
Year of designation
The year in which a bathing water was officially designated by Defra.