Most lead contamination of drinking water occurs when soft acidic water corrodes lead or galvanized pipes or corrodes solder used in pipe fittings. Lead from solder can be confirmed by testing to see if tin is also present. Lead is used in insecticides and in high octane gasolines. Lead contamination may be present in water from industrial waste disposal or landfill leachate. The primary drinking water standard for mercury is 0.002 milligrams per liter.
Mercury can cause acute poisoning in a large dose.
Since mercury accumulates in body tissues, it can cause chronic effects to the nervous system, kidney or intestines at low doses over a long period of time. Mercury contamination of water is caused by industrial or agricultural wastes. Selenium in small amounts is beneficial to health. Levels over the primary drinking water standard of 0.01 milligrams per liter may cause nervous system disorders, skin problems and in extreme cases may be fatal. Selenium occurs naturally in drinking water, though in trace amounts only.