Disinfection with Chlorine

Chlorination is the process of adding chlorine to drinking water to disinfect it and kill germs. Different processes can be used to achieve safe levels of chlorine in drinking water. Chlorine is available as compressed elemental gas, sodium hypochlorite solution (NaOCl) or solid calcium hypochlorite (Ca(OCl)₂ ¹. While the chemicals could be harmful in high doses, when they are added to water, they all mix in and spread out, resulting in low levels that kill germs but are still safe to drink ².

Chlorine was first used in the U.S. as a major disinfectant in 1908 in Jersey City, New Jersey ³. Chlorine use became more and more common in the following decades, and by 1995 about 64% of all community water systems in the United States used chlorine to disinfect their water ³.

Safe drinking water

Current studies indicate that using or drinking water with small amounts of chlorine does not cause harmful health effects and provides protection against waterborne disease outbreaks ².

Your health

Your water company monitors water quality regularly to provide you with safe drinking water. Some people are more sensitive than others to chemicals and changes in their environment. Individuals who have health concerns should seek medical advice from their healthcare provider before contacting their local health department.

Contact your local health department for more information.

Dialysis patients

During dialysis, large amounts of water are used to clean waste products out of a patient’s blood. Dialysis centers must treat the water to remove all chemical disinfectants, including chlorine and chloramine, before the water can be used for dialysis. Home dialysis users should consult the machine manufacturer for instructions on how to properly treat their water before use.

Chlorine levels up to 4 milligrams per liter (mg/L or 4 parts per million (ppm) are considered safe in drinking water. At this level, no harmful health effects are likely to occur ².

The U.S. Environmental Protection Agency (EPA) allows drinking water treatment plants to use chloramine and chlorine to disinfect drinking water. Water system pipes develop a layer of biofilm (scum) that makes killing germs more difficult ⁵. Water providers may temporarily switch from chloramine to chlorine disinfection to help remove this scum layer.

Chlorinated water can taste and smell different than untreated water ¹. Some people like the taste and smell of chlorinated water, and others do not. Taste and smell problems may arise depending upon the water quality and amount of chlorine in the water ⁶.

Chlorine and chloramine are toxic to fish, other aquatic animals, reptiles, and amphibians ⁷. Unlike humans and other household pets, these types of animals absorb water directly into the blood stream ⁷. Don’t keep these animals in water that contains these disinfectants. Chlorine can be removed from water by letting it sit out for a few days or by buying a product at your local pet store that removes the chlorine. Ask your local pet store about methods of removing disinfectants from water for these pets.

The small amount of chlorine added to water will not affect other pets (such as mammals and birds) and can be used regularly for watering and bathing animals.

Plants are not harmed by water treated with chlorine.