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Chlorination: The Addition
by Stephen K. Wiman, PhD of Goodwater Company, Santa Fe, New Mexico
“Chlorination” involves the addition of chlorine to water for the purpose of eliminating pathogenic (diseasecausing)
microorganisms. Chlorination also provides protection against (other) disagreeable tastes and odors,
eliminates slime bacteria, mold and algae, removes chemical compounds that inhibit disinfection and helps
remove iron and manganese from water. In 1997, the editors of LIFE Magazine stated that the filtration of
drinking water plus the use of chlorine are probably the most significant public health advances of the millennium.
Prior to 1908 and the onset of widespread and routine treatment of drinking water with chlorine, waterborne
diseases extracted a heavy toll in terms of illnesses and death in the US. Today, most water-related disease
outbreaks in the U.S. are associated with disinfection failure, water main breaks or natural catastrophes. How
fortunate we are in this country. On a global scale, 1.8 billion people lack access to safe drinking water and some
3.4 million people, mostly children under five, die every year from water- and sanitation-related diseases (World
Health Organization).
| DISEASE CAUSATIVE |
ORGANISM |
SOURCE OF
ORGANISM IN
WATER |
BACTERIA |
Cholera |
Vibrio cholerae |
Human feces |
E. coli |
Escherichia coli |
Ruminant animal and
pig feces. Birds. |
Salmonellosis |
Salmonella sp. |
Animal or human feces |
Typhoid |
Salmonella typhi |
Human feces |
VIRUS |
Infectious hepatitis |
Hepatitis A (HAV) |
Human feces |
PARASITES |
Amoebic dysentery |
Entamoeba histolytica |
Human feces |
Cryptosporidiosis |
Cryptosporidium sp. |
Animal or human feces |
Giardiasis |
Giardia lamblia |
Animal or human feces |
Table 1 - Globally Common Illnesses Caused by Waterborne Organisms
Drinking water pathogens can be classified in three broad categories: bacteria, viruses and parasitic protozoa.
See Table 1. Bacteria and viruses contaminate both surface and ground water and parasitic protozoa occur
predominantly in surface water. Chlorination is very effective at eliminating microorganisms in general; but it is
not a panacea, as some emerging pathogens such as the protozoan parasites Cryptosporidium and Giardia are
resistant to chlorination and must be removed by physical filtration. So if chlorine is so effective with
microorganisms, why does it not harm humans when we ingest chlorinated drinking water? One theory is that
food in our stomachs and the chemical composition of our intestinal tract quickly neutralize the chlorine and only
allow very low chlorine concentrations to exist.
Effective chlorine disinfection is a skillful balance of the overall water chemistry, pH and contact time. The water
utility must ensure that the water system has a suitable concentration of chorine for the appropriate period of time.
Water utilities need to diligently monitor chlorination to ensure that their equipment is working and that they are
providing potable water to their customers. To ensure continued protection against harmful organisms, the EPA
requires that residual chlorine remain in the transmission lines all the way to consumers’ taps. This is particularly
important for cities with aging water infrastructure.
The significance and success of chlorinating drinking water is unquestionable, but the story is not all good news.
Some critics argue that we do not use chlorine because it is the safest or even the most effective means of
disinfection, but simply because it is the least expensive alternative. There is also widespread concern about the
risk of inhaling chlorine while showering and the adverse effects on skin and hair. And the objectionable taste of
chlorine is thought to be a factor for some people who choose to hydrate with less healthful beverages.
But perhaps the biggest concern about chlorination is that the process can result in the formation of a group of
disinfection byproducts (DBPs) known as Trihalomethanes (THMs) and Haloacetic Acids (HAAs) , which are
formed, along with other disinfection byproducts, when chlorine or other microbial disinfectants react with naturally
occurring organic and inorganic matter in water. The number and nature of DBPs make it impossible to
characterize fully all of the byproducts formed during the treatment of drinking water. In a study commissioned by
the EPA, more than 500 disinfection byproducts were identified and a short list of fifty DBPs was created for future
investigation as health risks. Currently, four disinfection byproducts are regulated by the EPA, under
amendments to the Safe Drinking Water Act.
THMs and HAAs are potentially carcinogenic and have received widespread attention. If organic materials are
not removed from surface waters, the production of THMs is actually greater than with subsurface (aquifer) water
because of the relative higher organic content of surface waters. Water utilities remove organic material from the
source water before disinfection to minimize DBP formation as it is more cost-effective to reduce formation of
DBPs than to remove them from the treated water.
The controversies involved with chlorination of drinking water are largely about managing the portfolio of risks of
microbiological versus chemical contamination, but chlorination in some form to eliminate microbial threats is here
to stay in municipal systems. The best health protection we can have is to consider the options for reducing
chlorine within our homes. In future column articles, we will explore the options for removing chlorine and the
claims and the facts of what these methods will and will not remove in addition to chlorine.
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