Sources of lead in drinking water
Most lead contamination of drinking water takes place at some point in the water delivery system. This occurs as a result of corrosive water -- water that dissolves materials with which it comes in contact. Materials in the water delivery system that may contain lead include service connections, pipes, solder, and brass fixtures.
The natural mobility of lead in the environment is low, owing to the low solubility of this element in water. However, concentrations as high as 100 parts per million dissolved lead have been measured in rain and snow in areas of substantial air pollution. Regulation of leaded gasoline has significantly reduced lead aerosols from a peak of about 253,000 metric tons of lead in 1970, but large amounts continue to be released into the atmosphere in the smelting of ores and burning of coal.
It was common in some areas of the country to use lead pipes for interior plumbing through the early 1900s. Lead piping was also used for service connections to join residences to public water supplies. Copper piping replaced lead piping, but lead-based solder continued to be used to join copper piping until the U.S. Environmental Protection Agency (EPA) published a public drinking water rule in 1991 that emphasized eliminating lead from components of the water delivery system.
Today, many household faucets, plumbing fittings, and check valves are manufactured with brass parts, which contain some lead to make casting easier and the machining process more efficient. The lead content of brass plumbing components is now restricted to 8 percent, but even at this low level, lead can be leached from new brass faucets and fittings.
Some private wells may have submersible pumps containing brass capable of leaching lead. Some well screens also may contain lead or were installed with a “lead packing collar.” Potential lead contamination also exists if the well is a driven, sandpoint well and lead shot was poured into the well to keep out sand or clear the screen. In other wells, lead wool was used.
The characteristics of water vary greatly, and several factors cause water to be corrosive, including low pH (less than 7.0), high temperature, very low or very high total dissolved solids (TDS) content, and high amounts of dissolved oxygen or carbon dioxide. Naturally soft water is generally more corrosive than hard water because it lacks calcium carbonate, which produces scaling that protects pipes. Softer water also tends to be more acidic. Treating naturally hard water with an ion exchange water softening unit, reverse osmosis unit, or distillation unit may change the water chemistry enough to increase the water’s ability to dissolve lead.
Lead does not noticeably alter the taste, color or smell of water. The only way to know the concentration of lead in water is through sampling and laboratory testing.
Potential health effects from lead in drinking water
Lead accumulates in the body until it reaches toxic levels. It can be absorbed through the digestive tract and lungs and is carried by the blood throughout the body. The severity of the effects of lead poisoning varies depending on the concentration of lead in the body.
Excess lead in the human body can cause serious damage to the brain, kidneys, nervous system, and red blood cells. A child’s mental and physical development can be irreversibly stunted by lead poisoning. Lead poisoning can contribute to lower IQ levels, shortened attention spans, and increased behavior problems. While some effects of lead poisoning may diminish if exposure is reduced, others are irreversible. Young children, infants and fetuses are particularly vulnerable to lead poisoning. Lead in drinking water is not the predominant source of lead poisoning, but it can increase total lead exposure, particularly the exposure of infants who drink baby formulas and juices mixed with contaminated water.
Testing for lead in drinking water
Water supplied by public water systems is regulated by the U.S. Environmental Protection Agency (EPA). Sampling at the tap is required. EPA has established a primary drinking water standard for lead of 15 micrograms per liter (µg/l), which can also be expressed as 15 parts per billion (ppb). This amount is equivalent to 0.015 milligrams per liter (mg/l), which can also be expressed as 0.015 parts per million (ppm). When the lead concentration exceeds 15 ppb in over 10 percent of the homes tested, the public water supplier must initiate actions to reduce the lead concentration.
It is the voluntary responsibility of private water supply users to have their water tested and ensure that the water supply is safe for consumption. Private water supply users should have their water tested at a state-certified water testing laboratory. Test kits and dip strips available for do-it-yourself lead testing outside of a laboratory environment are not recommended. These kits may not provide accurate and reliable lead measurement. The standard set for public water supplies should be used as a guideline to evaluate risks from a private water supply.
In general, water that comes in contact with lead in plumbing will continue to dissolve it over time. For this reason, the highest lead concentration in drinking water will result from water that has sat motionless in the plumbing system, in contact with lead-containing components, for an extended period of time (e.g., several hours or overnight). To evaluate the household’s highest lead concentration, a water sample should be collected after the water has sat motionless in the plumbing system, in contact with suspected lead-containing components, for several hours.
A second sample collected after the tap has run for at least five minutes and the water has become noticeably colder will indicate the lead concentration that is present in the water before it enters the household plumbing.
Options for lead in drinking water
A public water system exceeding the EPA action level is required to take action to reduce lead levels.
If water tests indicate lead is present in drinking water and testing determines the source is household plumbing, first try to identify and eliminate the lead source. In addition, consider the corrosivity factor of the water and try to adjust it if possible. If neither is possible or cost-effective, disposing the water that has sat motionless in the plumbing system, in contact with lead-containing components for an extended period of time, may be an option. This is especially true in situations where the first water sample tested contained a high lead concentration and the second sample tested contained a low lead concentration. In addition, avoid cooking with or consuming water from hot-water taps. Hot water dissolves lead more readily than cold water.
There are several treatment methods suitable for removing lead from drinking water, including reverse osmosis, distillation and carbon filters specially designed to remove lead. Typically these methods are used to treat water at only one faucet. Simply boiling water does not remove lead. Another option may be to use bottled water for cooking and drinking.