A heavy metal that can be introduced into the water supply through the discharge of refineries and factories, runoff from landfills and croplands, and also from improperly discarded objects, especially electronics and items such as dry-cell batteries, thermometers and fluorescent light bulbs. If mercury poisoning occurred, it could damage the nervous system, impair hearing, speech, vision and gait, produce involuntary muscle movements, and can corrode skin and mucous membranes if contact happens. Long-term consumption can lead to kidney problems.