Only a small percentage of it requires treatment before the water can be used in the home. Naturally occurring conditions requiring treatment include excessive hardness and high concentrations of elements such as iron, manganese, and sodium. In addition to these naturally occurring conditions, however, there is also the threat of contamination from man-made chemicals. Major sources of these potential groundwater contaminants are underground storage tanks, chemical spills, landfills, abandoned dumps, and pesticide and fertilizer applications. Determining the danger of these possible contaminants involves a process called risk assessment.
Risk is the probability of injury, disease, or death under specific circumstances.
Everything we do has some degree of risk. The risks associated with some activities can be accurately predicted by examining precise data. The risks associated with other activities, including the exposure to various chemicals, cannot be readily assessed and quantified. Historical data on risks of chemical exposure may involve a single, very high exposure that has resulted in an immediately observable form of injury. Assessment of the risks of chemical exposures that do not cause immediately observable forms of injury or disease is far more complicated.