What Are Chlorine Burns?

by Pure Water Annie

Gazette technical wizard Pure Water Annie addresses the perplexing questions about water treatment.

Once a year, usually in spring,  water suppliers that normally disinfect their product with chloramine, a mixture of chlorine and ammonia, perform a cleaning procedure known as a “chlorine burn.”  The purpose is simply to clean out the pipes, ridding the distribution system of film and debris that has built up.

The clean-out is accomplished by simply switching disinfectants from chloramine to straight chlorine for a time, and usually upping the dosage a bit to speed things along. Compared with chlorine, chloramine is a rather weak disinfectant.  Its weak performance allows sludge and scum, bacterial film, to build up in pipe walls and crevices.  The yearly purge, or “burn,” with straight chlorine cleans things out.

Chloramine is substituted for chlorine as the regular disinfectant in an increasing number of city water systems. The switch from chlorine to chloramine has been going on over a number of years as suppliers seek ways to stay in compliance with EPA standards for DBPs,  disinfection by-products, that are produced as a consequence of chlorination. Some DBPs are known carcinogens, and EPA requires suppliers to monitor them.  Chloramine, a weaker disinfectant, does not produce DBPs.

Are chlorine burns a good idea?  Good or bad, they are necessary, since without a periodic cleanout, buildup in pipes would create significant problems for the water system.  The practice does call into question, however, the wisdom of using chloramine rather than chlorine in the first place, since, as many argue, the burn and subsequent purging of pipes creates elevated levels of disinfection by-products in the system and higher than normal chlorine discharge into lakes and streams. In other words, for a short time we get concentrated doses of disinfectants and byproducts, which may be worse than what we would have with chlorine as the regular disinfectant.

The moral: With a good carbon filtration system in your home, you won’t even know when the burn takes place.  The elevated chlorine levels, murky water, and dislodged sediment that your neighbors are complaining about, you won’t even notice.