Water quality can be negatively impacted by natural factors or by human actions. Many naturally occurring substances in groundwater are good for you. However, some minerals give water undesirable characteristics such as unpleasant taste, odor, appearance or hardness.

Any undesirable or harmful substance in groundwater is considered contamination. Human activities, such as dumping or spilling toxic chemicals on the ground, can result in groundwater contamination when those chemicals soak into the ground. Leaking landfills or underground storage tanks can introduce contaminants directly into the water supply, as can dumping chemicals down a well or cistern. Some of the other factors that locally contribute to groundwater contamination include:

• Sewage, septic tanks and sludge from wastewater treatment or industrial processes.
• Animal feedlots.
• Runoff of salts and automobile fluids from roads and parking lots.
• Mining and quarrying (chemicals used in the mining process or dumping wastes into old mining pits).
• Landfills and dumps.
• Overuse of fertilizers and pesticides.

Groundwater contamination also can occur when surface waters like lakes and rivers are contaminated. Because surface water and groundwater interact with each other, harmful substances can move from one to the other.