Chlorine: Definition & Technical Guide
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Chlorine is a chemical disinfectant added to municipal water supplies to kill bacteria, viruses, and other pathogens during treatment and to maintain residual protection as water travels through distribution pipes to homes and businesses. Chlorine is the most widely used water disinfection method in the United States, though its presence in household water affects taste, odor, and the longevity of plumbing components, leading many homeowners to install filtration systems that remove it at the point of use.
Residual Disinfection, Disinfection Byproducts & Pipe Material Effects
Water utilities use chlorine because it is effective, inexpensive, and maintains a measurable residual concentration throughout the distribution system. This residual is critical because it continues to neutralize pathogens that may enter the water through pipe breaks, cross-connections, or biofilm growth during the journey from the treatment plant to the tap. The EPA requires detectable chlorine residual at all points in the distribution system.
Two forms of chlorine disinfection are used in municipal water treatment. Free chlorine (hypochlorous acid and hypochlorite ion) provides rapid disinfection and a strong residual but reacts with natural organic matter to form disinfection byproducts (DBPs) including trihalomethanes (THMs) and haloacetic acids (HAAs), which are regulated by the EPA due to potential long-term health effects. Chloramine, formed by combining chlorine with ammonia, produces fewer DBPs and maintains a more stable residual over longer distances. Many large water utilities use chloramine as their primary disinfectant.
In plumbing systems, chlorine and chloramine affect certain materials. Chlorine accelerates the degradation of natural rubber seals, gaskets, and toilet flappers. It attacks the polymer structure of polybutylene pipe, contributing to the failure mode that led to its removal from plumbing codes. Thin-film composite reverse osmosis membranes are damaged by chlorine and require carbon pre-filtration for protection.
Free Chlorine, Chloramine, Chlorine Dioxide & Superchlorination
Free chlorine is elemental chlorine dissolved in water, available as chlorine gas, sodium hypochlorite (liquid bleach), or calcium hypochlorite (granular). It provides the most aggressive disinfection but has higher DBP formation potential.
Chloramine (monochloramine) is formed by adding ammonia to chlorinated water. It provides a stable, long-lasting residual with lower DBP formation and is used by many large water utilities.
Chlorine dioxide is an alternative disinfectant that does not form THMs or HAAs. It is used by some utilities as a pre-oxidant or primary disinfectant but does not maintain a distribution residual as effectively as chlorine or chloramine.
Superchlorination is the temporary application of high chlorine doses (5-20 mg/L) to new piping or repaired water mains to sterilize them before placing in service. The chlorine is flushed out before the water reaches consumers.
Carbon Filtration, Pipe Disinfection & Water Treatment Services
Chlorine removal is one of the most common reasons homeowners install water filtration. Bonded Plumbworks’ water filtration services include whole-house activated carbon systems that remove chlorine and chloramine before water reaches any fixture, protecting both water taste and plumbing components.
During repiping services, new piping must be flushed and disinfected per code requirements before being placed in service. Bonded Plumbworks follows the applicable state building codes’s disinfection protocols, which reference AWWA C651 for water main disinfection procedures, to ensure new piping delivers safe, clean water from day one.
EPA MRDL 4.0 mg/L, AWWA C651 & NSF/ANSI 42 Standards
The EPA Maximum Residual Disinfectant Level (MRDL) for chlorine is 4.0 mg/L and for chloramine is 4.0 mg/L. The EPA regulates THMs at a maximum of 80 ug/L and HAAs at 60 ug/L. AWWA C651 covers disinfection of water mains. NSF/ANSI 42 certifies filters for chlorine taste and odor reduction. NSF/ANSI 401 addresses emerging contaminants including chloramine.
Aquasana, Pentair & Culligan Chloramine Filtration Systems
Aquasana manufactures whole-house carbon filtration systems optimized for chloramine removal. Pentair produces catalytic carbon filters that break down chloramine more effectively than standard carbon. Culligan offers point-of-entry systems with chlorine and chloramine reduction. SpringWell and Pelican produce salt-free systems with integrated carbon filtration.