Pure water contains nothing but the essential chemical elements of water. Drinking water usually carries a certain amount of minerals, which it acquires from its source, treatment, storage, distribution, and household plumbing conditions. These minerals and elements generally occur at very low levels and do not pose a significant risk to health. For more information click on Drinking Water Standards.
A wide variety of chemicals and compounds can become groundwater contaminants if discharged to the subsurface environment. They are inorganic compounds, organic and synthetic compounds, such as pesticides, and other contaminants. Because drinking water systems get their water from groundwater (and SW) sources, once the source becomes contaminated, the drinking water can also become contaminated.
The following table shows the primary and secondary water contaminants, divided in inorganic and organic elements.
For every substance the Maximum Contaminant Level (MCL) is quoted: that is the maximum permissible level of a contaminant in water that is delivered to any user of a public water system. It is based on scientific research, which concludes that greater concentrations could cause health problems in humans.