Chlorine is a disinfectant (chemical) that is added to our drinking water to reduce or get rid of bacteria and viruses that may be in our water supply. According to Health Canada, adding chlorine to drinking water greatly reduces your risk of getting a waterborne illness.
These illnesses include cholera, giardiasis and sickness caused by the bacteria Escherichia coli (E.coli). E. coli can cause diarrhea, abdominal cramps and sometimes more serious illness.
When chlorine mixes with organic matter (such as dead leaves and soil), it forms new chemicals that remain in the water. These are called chlorination by-products.
The International Agency for Research on Cancer (IARC) classifies some chlorination by-products as possible causes of cancer, specifically bladder cancer.