Contaminants can be grouped into five categories. Microorganisms such as total coliform, giardia, and viruses generally come from human or animal waste and cause various diseases, including gastrointestinal illness. Other IOCs, such as lead and copper, when present in public water supplies, have usually been introduced by humans.
Inorganic contaminants can damage the nervous and circulatory systems and other organs.
Examples include benzene, trichloroethylene and chloroform. VOCs can cause cancer and damage organs, especially those comprising the nervous and circulatory systems. This category includes many pesticides and herbicides. These chemicals can cause cancer and damage organs, especially those comprising the nervous and circulatory systems. Radiochemicals include naturally-occurring chemicals such as radium and radon, as well as chemicals from nuclear activities.