Prior to reaching aquifers or other natural bodies of water like rivers, lakes, estuaries, and seas, wastewater treatment, sometimes referred to as sewage treatment, removes contaminants from wastewater or sewage. Since there is no such thing as pure water in nature (i.e., outside of chemical labs), any differentiation between clean and contaminated water depends on the kind and quantity of pollutants present in the water as well as the use to which it will be put.