What is a lead service line in water distribution, and what is its effect on health?

Lead service line constitutes part of the drinking water distribution network in some parts of the world, and its use comes from the antiquated concept of providing disinfection to the drinking water distributed in a typical city’s vast distribution network. Specifically, water that leaves the drinking water treatment plant would need to pass through a lengthy distribution network before reaching individual homes, and the process meant that potable water (i.e., disinfected water ready to drink) could become contaminated in the distribution network. Typically, the residence time of potable water in the drinking water distribution network could be days or one week, depending on the demand for drinking water at specific parts of the distribution network.


Modern approaches for maintaining disinfection of potable water distributed in the drinking water distribution network comprise the addition of a disinfectant, monochloramine, into potable water. Briefly, monochloramine kills bacteria and fungi; thereby, ensuring the drinking water is safe for consumption even after days of residence in the drinking water distribution system. The level of monochloramine in the drinking water is known as disinfectant residual, and protects the potable water from contamination by bacteria, fungi and viruses that could enter the distribution network. Prior to leaving the drinking water treatment plant, the potable water enters a final phase of disinfection through pumping in chlorine and irradiating the water with ultraviolet light.


Reaction between chlorine and ammonia lead to the formation of chloramine that could serve as a secondary residual disinfectant that protects the potable water against contamination in the drinking water distribution system. However, given the propensity of chlorine’s reaction with ammonium compounds to form disinfectant byproducts such as trihalomethanes, amount of chlorine added to potable water in the final polishing step prior to distribution in the drinking water distribution network needs to be carefully titrated. Nevertheless, monochloramine remains the first choice for water treatment companies in conferring a chlorine residual in water for maintaining the microbiological quality of water for drinking purposes. By having a chlorine residual, which is not sufficient to induce harm in human beings, potable water could be free of viable microorganisms for substantial amount of time (maximum: a few days) in the water distribution network.


On the other hand, is lead service line safe in maintaining the microbiological and chemical quality of drinking water distributed in the distribution network? The answer is no. Because, while the small amount of lead that leaches from the pipeline may help kill microbes detrimental to health, lead is also a known neural poison with significant health effects on various organs of the body. Prolonged or chronic exposure to lead would incur substantial health impacts on organs such as the brain, skin, liver and kidney. Hence, lead service line would progressively be replaced by plastic or copper pipes in remaining areas of the world with antiquated water distribution network. Given the significant health impacts of lead, U.S. Environmental Protection Agency has promulgated the “Lead and copper rule” to safeguard the quality of drinking water distributed in the distribution network after treatment.


Collectively, lead service lines are present in some parts of the world with aged drinking water distribution system. Originally used for maintaining safe drinking water in long pipelines connecting the rural drinking water treatment plants to the crowded cities, lead service lines have outlived their usefulness given the availability of new and better ways for maintaining the microbiological quality of drinking water distributed in a city’s distribution network. For example, addition of chlorine into potable water at the finishing step of drinking water treatment helps confer drinking water with a chlorine residual useful for killing microbes with detrimental effects on health. Additionally, the monochloramine formed through reaction of chlorine with ammonium compounds does not result in elevated concentrations of trihalomethanes, that as disinfection byproducts, has been linked to chronic health effects. Low concentration of monochloramine, however, is not linked to significant health risks. Hence, lead leached from lead service line used in distributing drinking water is a big health threat, and lead service line usage is declining across the world.


Category: environment, health,

Tags: microbiological quality, lead, lead service line, drinking water, chlorine residual, potable water, trihalomethanes, disinfection byproducts,






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