A water contaminant is a substance which is found in water that has the potential to pose a risk to public health at certain levels. Some contaminants occur naturally in the environment and seep into water sources through erosion. Unfortunately, many of the contaminants found in water are a result of human activities. The industrial wastes from factories, refineries, mines and mills all contain harmful substances which can contaminate water sources.
Many water treatment plants use a combination of coagulation, sedimentation, filtration and disinfection to provide clean, safe drinking water to the public. Worldwide, a combination of coagulation, sedimentation and filtration is the most widely applied water treatment technology, and has been used since the early 20th century.