Impurities of drinking water are mainly of two types- chemical and biological.They may be natural or manmade.
Salts, pesticides, metals, nitrogen, bleach, toxins, human or animal drugs are chemical impurities.
Biological microorganisms such as bacteria, viruses, protozoa are of the second type of contaminants.
This impurity may cause many waterborne diseases like loose motion, cramping in stomach, diarrhoea, typhoid, cholera, hepatitis etc.