Wastewater (or waste water) is any water that has been affected by human use. Wastewater is "used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff or stormwater, and any sewer inflow or sewer infiltration".[1] Therefore, wastewater is a byproduct of domestic, industrial, commercial or agricultural activities. The characteristics of wastewater vary depending on the source. Types of wastewater include: domestic wastewater from households, municipal wastewater from communities (also called sewage) and industrial wastewater from industrial activities. Wastewater can contain physical, chemical and biological pollutants.
Households may produce wastewater from flush toilets, sinks, dishwashers, washing machines, bath tubs, and showers. Households that use dry toilets produce less wastewater than those that use flush toilets.
Wastewater may be conveyed in a sanitary sewer that conveys only sewage. Alternatively, it can be transported in a combined sewer that conveys both stormwater runoff and sewage. After treatment at a wastewater treatment plant, treated wastewater (also called effluent) is discharged to a receiving water body. The terms "wastewater reuse" or "water reclamation" apply if the treated waste is used for another purpose. Wastewater that is discharged to the environment without suitable treatment causes water pollution.
In developing countries and in rural areas with low population densities, wastewater is often treated by various on-site sanitation systems and not conveyed in sewers. These systems include septic tanks connected to drain fields, on-site sewage systems (OSS), vermifilter systems and many more.
Sources of wastewater include the following domestic or household activities:
Human excreta (feces and urine) often mixed with used toilet paper or wipes; this is known as blackwater if it is collected with flush toilets
Washing water (personal, clothes, floors, dishes, cars, etc.), also known as greywater or sullage
Surplus manufactured liquids from domestic sources (drinks, cooking oil, pesticides, lubricating oil, paint, cleaning liquids, etc.)
Activities producing industrial wastewater include:
Industrial site drainage (silt, sand, alkali, oil, chemical residues);
Industrial cooling waters (biocides, heat, slimes, silt)
Industrial processing waters
Organic or biodegradable waste including waste from hospitals, abattoirs, creameries, and food factories.
Organic or non bio-degradable waste that is difficult-to-treat from pharmaceutical or pesticide manufacturing
Extreme pH waste from acid and alkali manufacturing
Toxic waste from metal plating, cyanide production, pesticide manufacturing, etc.
Solids and emulsions from paper mills, factories producing lubricants or hydraulic oils, foodstuffs, etc.
Water used in hydraulic fracturing
Produced water from oil & natural gas production
Other related activities or events:
Urban runoff from highways, roads, carparks, roofs, sidewalks/pavements (contains oils, animal feces, litter, gasoline/petrol, diesel or rubber residues from tires, soapscum, metals from vehicle exhausts, de-icing agents, herbicides and pesticides from gardens, etc.)
Agricultural pollution, direct and diffuse
Wastewater can be diluted or mixed with other types of water through the following mechanisms:
Seawater ingress (high volumes of salt and microbes)
Direct ingress of river water
Rainfall collected on roofs, yards, hard-standings, etc. (generally clean with traces of oils and fuel)
Groundwater infiltrated into sewage
Mixing with other types of wastewater or fecal sludge
