关键词：饮用水 用水 水中
Drinking Water: Lead
Too much lead in the human body can cause serious damage to the brain, kidneys, nervous system and red blood cells.
Lead in Drinking Water
Small quantities of lead can be a serious health concern, especially for children. Sources of lead in the environment include lead-based paint; lead contaminated soil, air and dust; lead contaminated food; imported food in lead-soldered cans; non-FDA regulated ceramics with lead glazes; leaded crystal and lead contaminated drinking water.
Lead rarely occurs naturally in water. Most lead contamination takes place at some point in the water delivery system. This occurs as a result of corrosion, the reaction between the water and lead in parts of the water delivery system. Materials in the water delivery system which may contain lead include service connections, pipes, solder and brass fixtures.
Water's characteristics vary: some water is naturally more corrosive than others. Several factors cause water to be corrosive including acidity (low pH), high temperature, low total dissolved solids (TDS) content and high amounts of dissolved oxygen or carbon dioxide. Generally, naturally soft water is more corrosive than hard water, because it is more acidic and has low TDS. Softening naturally hard water with an ion exchange water softening unit does not appreciably change the corrosivity of the water, resulting in little, if any, effect on the water's ability to dissolve lead.
Lead in drinking water from plumbing or fixtures is most often a problem in either very old or very new houses.
Through the early 1900's it was common in some areas of the country to use lead pipes for interior plumbing. Lead piping was also used for the service connections used to join residences to public water supplies. Lead piping is most likely to be found in homes built before 1930. Copper piping replaced lead piping, but lead-based solder was used to join copper piping. It is likely lead-based solder was used in any home built before 1988.
Today, brass materials are used in nearly 100 percent of all residential, commercial, and municipal water distribution systems. Many household faucets, plumbing fittings, check valves and well pumps are manufactured with brass parts. While brass contains 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. Even at this low level, however, lead can be leached from new brass faucets and fittings. Eventually, if the water is not corrosive, hard water minerals deposit on the interior of plumbing. These deposits form a calcium carbonate lining inside pipes and fittings which protects against lead contamination. It may take up to five years for an effective calcium carbonate lining to form. Softening naturally hard water with an ion exchange water softening unit can either prevent or dissolve the calcium carbonate scale, eliminating its possible protective effect.
Some private wells may have submersible pumps containing brass or bronze 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 has been "shot" to clear the screen. Lead shot was sometimes poured into a well to keep out sand. In other wells, lead wool was used. None of these practices are recommended and driven, sandpoint wells are not allowable under Nebraska well construction regulations.
Older water coolers with lead-lined tanks are anot
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