Trace amounts of metals are common in water, and these are normally not harmful to your health. In fact, some metals are essential to sustain life. Calcium, magnesium, potassium, and sodium must be present for normal body functions. Cobalt, copper, iron, manganese, molybdenum, selenium, and zinc are needed at low levels as catalysts for enzyme activities. Drinking water containing high levels of these essential metals, or toxic metals such as aluminum, arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver, may be hazardous to your health. (reference 80)
Metals in your water supply may occur naturally or may be the result of contamination. Naturally occurring metals are dissolved in water when it comes into contact with rock or soil material. Other sources of metal contamination are corrosion of pipes and leakage from waste disposal sites. Metals should be removed from drinking water if they are present at high enough levels to cause concern.
The health effects related to consumption of several metals are presented below. Keep in mind that research is still being conducted on the toxicity of most of these elements. Consult with a physician if your water contains metals and you suspect health problems related to metal consumption.
Methods for removal of some trace amounts of toxic metals include distillation, ion exchange, reverse osmosis, and activated carbon filtration. All systems are expensive to purchase and operate. They are normally installed only on the drinking water line.
If metals are present in water because of corrosion of pipes, there are several treatment options which are less expensive than those described above. If your water is acid (low pH), the best solution may be to neutralize (raise to pH 7) the water before it enters your home plumbing system. Special filters containing such materials as calcium carbonate (CaCO3), sometimes called calcite, or magnesium oxide (MgO), sometimes called magnesia, are available for neutralizing acid water. These filters will increase the hardness of your water, and they must be backwashed periodically.
Another neutralization technique involves addition of sodium carbonate (NaCO3), sometimes called soda ash, into the water system. This should be injected ahead of the pressure tank, and may be mixed with chlorine solution if chlorination is also used. Keep in mind that soda ash adds sodium to your water. To prevent corrosion by creating protective films on plumbing components, chemicals such as polyphosphates and silicates may be injected into the plumbing system. Non-corroding plumbing materials, such as plastic or polyvinyl chloride (PVC) may be used if old pipes must be replaced.
Metal concentrations in tap water are highest after water has rested in the plumbing system for a long time. Before drinking each morning, run your cold water several minutes to flush metals which have accumulated overnight. Elevated temperatures result in increased corrosion. Therefore, hot water heaters should be set only as high as is necessary. To be safe, water from the hot water tap should not be used for drinking or cooking.