Water industry terms A-Z

Annual return
South West Water is required to submit to the Environment Agency (EA) a report detailing number of spills for each overflow with EDM (Event Duration Monitoring), which occurred during the previous calendar year. We count spills using the 12/24 counting method, see ‘Spill’ for further information. 

Bathing season
The bathing season in England runs from 15 May to 30 September when we expect the most people at bathing waters. During the bathing season, water quality at designated bathing waters is monitored by the Environment Agency. 
 

Catchment
A sewage treatment works catchment is the area of sewerage draining to that sewage treatment works.
 

A river catchment is the area of land draining to that river. 

These catchments can also be divided in sub-catchments. 

Designated bathing water 
Bathing water designation in England is made by the Department of Environment Food and Rural Affairs (Defra). According to the Bathing Water Regulations 2013, a bathing water is defined as a body of water 'at which the Secretary of State expects a large number of people to bathe'. 

Drainage 
A collection of sewers, drains, and other engineering works designed to carry wastewater and stormwater away from a built-up environment. 

Event Duration Monitor (EDM) 
Event Duration Monitoring allows us to monitor how often and for how long storm overflows are used.

Foul water
Wastewater that comes from houses and businesses, e.g. from showers, toilets, washing machines etc. 

Groundwater 
Water that collects below the surface of ground in the soil and rocks.  

Hydrological continuity
The continuous distance from the overflow discharge point to the bathing water area by following the route of watercourses, such as rivers, estuaries and coastal environments.

Infiltration 
Where groundwater or seawater enters the sewerage system. This can be via unauthorised connections such as land drains as well as through small defects in pipes and manholes. 

Investment programme 
A collection of work that is designed to bring benefit to the environment, communities or services we provide. Our WaterFit programme sets out our commitments and plans to deliver more for our beautiful South West region. 

Misconnected pipes 
When a foul sewer is connected to a surface water sewer (or vice versa). This means that the sewer is transporting water it wasn’t designed to carry (e.g. foul sewage entering a surface water system or surface water entering a separate foul system). 

Non-foul flow 
Rainwater, surface water, groundwater and seawater. Note that grey water from sinks and showers is considered to be foul water. 

Non-sewage related wastewater 
Non-sewage wastewater incorporates all types of wastewater that do not contain human waste. That includes rainwater and stormwater from flooding, water from commercial activity like garages or laundrettes and water from industrial plants.  

Private sewerage 
A sewer for which the South West Water is not responsible. Generally, it is collectively owned and maintained by the owner(s) of the building(s) it serves. 

Pumping station 
A structure containing pumps and piping, valves and other mechanical and electrical equipment for pumping water, wastewater and other liquids up hills. There are separate pumping stations for each type of water. 

Resilience 
Resilience is our network’s ability to cope with, and recover from, changes that affect its performance. 

Rising main 
A rising main is a pressurised sewer pipe. It carries wastewater that is pumped from a pumping station to join with the main sewerage system. 

Runoff 
Rainwater that flows off a surface such as roads, roofs and fields to reach a drain, sewer or receiving water. 

Screen/screening 
A device with openings, generally of uniform size, used to retain or remove suspended or floating solids in flowing water or wastewater. For example, a screen at a storm overflow retains sewage related debris in the sewer. 

Sewage treatment works 
A series of processes to remove debris and contaminants to provide a cleaner effluent that is suitable for releasing into the environment. The processes at a sewage treatment works depends on the size of the upstream catchment and the environment to which it discharges. 

Sewer related debris 
Substantial items of debris which are inappropriately flushed down the toilet, such as sanitary towels, tampons, cotton buds, condoms and other plastics. It can also refer to toilet paper. 

Sewer rehabilitation 
Methods used to improve the structure and watertightness of a sewer pipe and manholes. This can include pipe lining, pipe patching, resin injection sealing, concrete repairs, dig down repairs and partial replacement. 

Sewerage network 
All the sewers, pumping stations, treatment works and associated systems that transport and treat wastewater. 

Significant spill 
A discharge from an overflow is classed as significant when the volume exceeds a specified threshold. This threshold depends on the receiving water and has been determined by historic analysis and agreed with the Environment Agency. Generally, it is 50 metres cubed but can be larger. 

Spill 
When an overflow discharges wastewater or stormwater from the sewerage network to the environment. The number of spill events over a given period is called ‘spill frequency’. We count spills using the 12/24 counting method. This means we start counting when the first discharge occurs, any discharge (or discharges) in the first 12-hour block is counted as one spill. Any discharge (or discharges) in the next, and subsequent 24-hour blocks, are each counted as one additional spill per block. 

Storm Discharge 
When wastewater or storm water releases into the environment, via a permitted storm overflow. 

Storm overflow 
Storm overflows are built into the sewerage network and may operate automatically during heavy rainfall to protect properties from flooding. Storm overflows maybe within the sewerage network, also known as combined sewer overflows (CSOs), or at the sewage treatment works. Some storm overflows may be settled in a tank to provide a better quality discharge. 

Storm tank or storm water tank 
Tanks provide storage of stormwater during rainfall periods and return the stormwater back to the sewerage system when the rainfall has stopped. This reduces the use of storm overflows and can provide a better quality discharge when the overflow is from the top of the tank.  

Storm water 
A large volume of surface water / runoff resulting from rain or melting snow. 

Surface water network 
A drain or sewer system that has been designed to carry surface water only. 

Ultraviolet disinfection 
Treated wastewater is sometimes passed through ultraviolet light to reduce the number of harmful bacteria and viruses like cryptosporidium. 

Wastewater 
Any water that has been used or drains into the wastewater network. 

Watercourse 
A watercourse is defined as any channel through which water flows and can be open or enclosed underground as a culvert. Watercourses may be classified as either main rivers or ordinary watercourses. 

WaterFit 
WaterFit is the next stage in our environment strategy, accelerating and expanding plans to protect and enhance the South West’s water for future generations. See: www.southwestwater.co.uk/waterfit 

WaterFit Live 
WaterFit Live allows you to see whether any of our overflows near bathing beaches may temporarily affect bathing water and shows our investment information along with other helpful resources relating to storm overflows www.southwestwater.co.uk/waterfitlive 

Your Beach, Your Say, Our Investment 
If you’re a community group or part of a local network and would like to have your say, or provide feedback about your local beach, visit ‘Your Beach, Your Say, Our Investment’.

 

Organisations 

Consumer Council for Water 
Defra (Department for Environment Food and Rural Affairs) 
Environment Agency 
OFWAT 
Water UK