What is wastewater?

Dirty water that is sent down our drains and toilets is called wastewater. It contains materials that need to be removed before the water is returned to the natural environment. These can include:

  • solids and organic matter
  • pathogens (disease causing organisms)
  • nutrients (nitrogen, phosphorus, etc.)
  • chemicals (cleaners, disinfectants, medications)
  • heavy metals (mercury, lead, etc.)


Ensuring that our wastewater is treated is important for a variety of reasons. Untreated wastewater can pose a health risk to people, pets and wildlife that drink or come in contact with it. Disease causing microorganisms, toxic contaminants, and levels of nitrates high enough pose health threats can be found in untreated wastewater.

Untreated wastewater can also be an environmental threat to surface and groundwater quality due to its organic matter and nutrient content (phosphorus, nitrate and ammonium) and the household synthetic cleaning products which it may contain. It can fertilize water bodies, a process called eutrophication, degrading water quality by causing noxious blooms of algae and excessive pondweed growth, reducing clarity and oxygen levels, and smothering habitat. All of these effects typically lead to degraded food webs and fisheries.

Learn more about the City of Superior's wastewater and stormwater treatment in this slideshow (exit). And learn how the City of Duluth has successfully dealt with sewage overflows in this 2015 Duluth News Tribune article (link to pdf).