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Last edited 01 Jan 2021
The term ‘waste water’ (or wastewater) is sometimes used to refer to all water that has been used in homes, businesses, industry, agriculture and so on, as well as rain that falls on roofs, roads, and landscape, that then enters the sewerage system.
However, the term waste water is more accurately used to refer only to water that has been used in homes, businesses, industry, agriculture and so on, whilst water from rainfall is referred to as ‘surface water run-off’. NB The term or ‘sewage’ refers specifically to a mixture of waste water and excrement.
Types of sewer include:
- Sanitary sewers: Used solely for carrying sewage.
- Surface water sewers: Used solely to drain surface water run-off.
- Combined sewers: Used to carry both sewage and surface water run-off.
- Effluent sewers: Sometimes referred to as Septic Tank Effluent Drainage (STED) or Solids-Free Sewers (SFS)).
NB A drain is a pipe that serves only one building waste water to a sewer. A lateral drain is a section of drain positioned outside the boundary of a building, connecting with the drains from other buildings to become a sewer.
The treatment of waste water generally involves:
- Primary settlement.
- Sludge treatment and biological treatment.
- Final settlement.
- Return to watercourses (where it may be referred to as effluent, secondary effluent, or treated effluent).
Where properties are not connected to the sewerage infrastructure they may have septic tanks. These are tanks installed underground that separate waste water into solids and water that can be safely discharged into a septic drain field (seepage field or leach field). Material that does not break down naturally in septic tanks must be periodically removed and disposed of.
Rather than discharging directly into sewers, surface water run-off may be collected and stored. This can help reduce flooding during heavy rainfall events. Sustainable urban drainage systems (SuDS) aim to mimic 'natural' drainage by adopting techniques to deal with surface water run-off locally, through collection, storage, and cleaning before allowing it to be released slowly back into the environment.
Suitable surface water run-off (sometimes referred to as ‘grey water’ as it excludes sewage), such as run-off from the roofs of buildings, may be ‘reclaimed’ and treated to be re-used in WCs, urinals irrigation, washing machines and so on.
The terms black water, brown water, foul water, or sewage, refer to water that has come into contact with faecal matter or urine. Black water can be harmful to health and may contain bacteria, viruses, protozoa and parasites. Globally, most black water is discharged back into the environment without having been treated. This results in significant environmental damage and health problems.
NB The SuDS Manual (C753), published by CIRIA in 2015 defines wastewater as: 'Water used as part of a process that is not retained but discharged. This includes water from sinks, baths ,showers, WCs and water used in industrial and commercial processes.'
The Scottish Building Standards, Part I. Technical Handbook – Domestic, Appendix A Defined Terms, defines wastewater as: ‘…water that is contaminated by use and normally discharged from a watercloset, shower, bath, bidet, washbasin, sink, washing machine, floor gully and similar facility and also includes rainwater when discharging in a wastewater drainage system.’
 Related articles on Designing Buildings Wiki
- Clarified water.
- Difference between drains and sewers.
- Foul water.
- Grease management.
- Hot water.
- Integrated water management.
- Mains water.
- Public sewer.
- Sanitary pipework.
- SO2 Scrubbers.
- Sustainable urban drainage systems SUDS.
- Types of water.
- Water quality.
- Water transfers and interconnections.
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