Chlorine FAQs

Why chlorinate tap water?

Introduced into the municipal water supplies in the United States in 1908, chlorine is a highly effective and inexpensive way to disinfect tap water. Without disinfecting municipal water, tens of thousands of people would die from disease-causing microorganisms, such as typhoid, cholera, and dysentery. Continuous chlorination has dramatically reduced these diseases to virtually nonexistent levels. Chlorine is now the most widely used disinfectant in the world. But while chlorination has helped save lives, there is growing evidence that chlorinated water could be very hazardous to human health.a

What are the health risks of chlorination?

Chlorine disinfectant can react with organic matter often found in water, such as algae and decaying plants, to produce hundreds of different types of chemical disinfection byproducts (DBPs), such as trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and Mutagen X (MX). These chemicals have been linked to serious health problems, including cancer, birth defects, and DNA damage.b

How much chlorine is in the water supply?

Because chlorine levels vary by region, the best way to determine levels for your region is to contact your local water supplier. Municipal water centers are legally required to provide an annual water quality report that details chlorine levels in your tap water. Additionally, affordable home test kits can also test for chlorine and other contaminates.c


a “A Giant Step for Public Health: Chlorination in Chicago and Jersey City.” The American Chemistry Council’s Chemistry Division. Accessed: June 6, 2010.

b “Disinfection By-Products in Drinking Water.” Environmental and Occupational Health, Division of Epidemiology. July 1999. Accessed: June

c “Questions and Answers on Health Effects of Disinfection Byproducts.” U.S. Environmental Protection Agency. May 2004. Accessed: June 6, 2010.