What is wastewater?

What is wastewater?

Wastewater is any water that has been used from human activities that happen at home or in the workplace. These activities produce used water that flows down a drain. Wastewater comes from several sources including the household, communities and industry. This used water is classified into graywater and blackwater based on what is in the water. Treating the wastewater is important for the safety of mankind and the environment.

wastewater from human activities

Wastewater from various sources

Wastewater is residential and nonresidential. It comes from domestic, municipal, community and industrial sources. Domestic wastewater is derived from household activities. Washing dishes or laundry, flushing the toilet, draining the bathtub, water going down the shower drain, and anything else that dirties the water in a household is considered domestic wastewater. It can include food scraps, soap, body waste, oils, soaps, and chemicals.

Municipal wastewater includes household wastewater and wastewater from community areas such as schools, restaurants, libraries and shopping centers. This wastewater may contain hazardous materials and requires special treatment or disposal. It is also known as sewage.

Industrial wastewater is a byproduct of water used in manufacturing such as making a commercial product or implementing a cleaning process. This type of wastewater is carefully managed. Wastewater discharges from industrial and commercial sources may contain pollutants at levels that could affect the quality of receiving waters or interfere with publicly owned treatment works (POTWs) that receive those discharges.1 The National Pollutant Discharge Elimination System (NPDES) permitting program establishes discharge limits and conditions for industrial and commercial sources with specific limitations based on the type of facility/activity generating the discharge.2

Types of wastewater

Wastewater is typically classified into either graywater or blackwater. While this is a basic classification, each state in the US and countries around the world define wastewater specifically.

Graywater is mildly used water; water not being discharged from the toilet or diapers. Examples of graywater is water from baths, showers, or lightly washing dishes. It may contain traces of dirt, food, grease, hair, and certain household cleaning products. Graywater can be reused to water plants in a garden.

Blackwater is the water that comes in contact with human waste. This also includes water from laundry that has been used to wash diapers or soiled clothes and bed linens. Wastewater from your kitchen sink is also treated as blackwater because it can be highly contaminated with food particles, cooking oil and grease. According to the EPA, ideally, blackwater should be retained and disposed of according to a land-based treated effluent reuse scheme.

What is in wastewater?

Wastewater is 99.9% water and 0.1% waste.

  • Solids in organic or inorganic form
    • Organic matter—the human wastes, paper products, detergents, cosmetics, foods described above
    • Inorganic minerals, metals, and compounds, such as sodium, potassium, calcium, magnesium, cadmium, copper, lead, nickel, and zinc
  • Gases that can collect near manholes, septic tanks or treatment plants
  • BOD (biochemical oxygen demand)—BOD is the amount of oxygen needed by aerobic bacteria to break down organic matter
  • Organisms—such as worms, bacteria and protozoa live in wastewater. They work to break down certain organic pollutants in the wastewater by consuming them.
  • Total suspended solids (TSS)—specific size and number of solids suspended in wastewater
  • Pathogens—viruses or bacteria that can cause diseases (i.e., E. coli, Coliforms)
  • Oil and grease
  • Nutrients—phosphorous and nitrogen in the form of phosphate and nitrate
  • Micropollutants—pharmaceuticals, personal care items, and ammonia-based fire retardants

Why is wastewater treated?

Treating wastewater helps our environment and our health. If wastewater is not treated, it can have negative and toxic effects on humans and the environment. In all but the most highly developed countries, the vast majority of wastewater is released directly to the environment without adequate treatment, with detrimental impacts on human health, economic productivity, the quality of ambient freshwater resources, and ecosystems.3


1, 2. Industrial Wastewater, National Pollutant Discharge Elimination System (NPDES), EPA, accessed February 13, 2020, https://www.epa.gov/npdes/industrial-wastewater
3.2017 UN World Water Development Report, Wastewater: The Untapped Resource, United Nations (UN) Educational, Scientific and Cultural Organization, accessed February 17, 2020, https://reliefweb.int/report/world/2017-un-world-water-development-report-wastewater-untapped-resource

More Wastewater Articles

The Basics

The Importance of Wastewater Treatment
Using PCR and qPCR in Water Treatment
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Total Suspended Solids (TSS) Method and Procedure
Chemical Oxygen Demand (COD) Methods and Procedure
Approved Analysis Methods for Ammonia
Understanding Oil and Grease EPA 1664
Predictive Maintenance with Affordable Thermal Imaging
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