10 Important Facts about Chlorine in Tap Water

  • Moderate to heavy consumption of chlorinated tap water by pregnant women has been linked with miscarriage, birth defects, heart problems, cleft palate, and major brain defects.a
  • The presence of chlorine in tap water has been linked to the dramatic rise of heart disease in the United States. Scientists argue that chlorine is a primary cause of the development of atherosclerosis, or hardening of the arteries.b
  • Studies show chlorinated water is toxic to human intestinal bacteria, the body’s natural flora that converts organic compounds in our food into necessary nutrients.b
  • The American Journal of Epidemiology contains one of a number of studies that report chlorine disinfection byproducts (DBPs) are responsible for the increase in rectal and bladder cancers.b
  • Several research journals, including Environmental Health Perspectives, call the chlorine disinfectant byproduct Mutagen X (or MX) one of the most deadly carcinogens in tap water.b
  • After large rainstorms, your municipal water center may add more chlorine to the water supply to treat potentially larger number of microorganisms due to runoff or sewage discharges.d
  • During the summer, surface water used for drinking contains more organic material and, as a result, DBP levels are often higher than they are in the fall and other times of the years.d
  • Chlorinated water increases the amount of heavy metals such as lead and copper that are leached from pipes into tap water.b
  • Because chlorine is a calcium antagonist, long-term consumption of chlorinated water has been linked to loss of calcium in bones. Chlorinated tap water has also been linked to childhood and adult asthma and allergies.b
  • The EPA allows a higher level of chlorine in tap water (4 parts per million/ppm) than the recommended chlorine levels for public swimming pools (1-3 ppm).c


a “Drinking Tap Water Disinfected with Chlorine May Harm Fetus, Study Suggests.” Science Daily. June 5, 2008. Accessed: June 4, 2010.

b Kahuna Kupua A’o, Lono. 2004. Don’t Drink the Water. Twin Lakes, WI: Lotus Press.

c “Pool Water Chemistry.” Pool and Spa. Accessed: June 7, 2010.

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