Frequent Questions

1. What are disinfectants like chlorine dioxide, how are they used, and what are their health effects in drinking water at levels above the maximum residual disinfectant level?

Disinfectant (Chemical Abstract Service Registry Number)

Definition and uses

Health Effects

Chloramine (as Cl2) (10599-90-3)

Chloramine (as CI2) is a water additive used to control microbes, particularly as a residual disinfectant in distribution system pipes. It is formed when ammonia is added to water containing free chlorine. Monochloramine is one form of chloramines commonly used for disinfection by municipal water systems. Other chloramines (di- and tri-) are not intentionally used to disinfect drinking water and are generally not formed during the drinking water disinfection process.

Some people who use water containing chloramine in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose, stomach discomfort or anemia.

Chlorine (as Cl2)(10049-04-4)

The gaseous or liquid form of chlorine (CL2) is a water additive used by municipal water systems to control microbes. It is relatively inexpensive and has the lowest production and operating costs and longest history for large continuous disinfection operations. Chlorine is a powerful oxidant.

Some people who use water containing chlorine well in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose. Some people who drink water containing chlorine well in excess of the maximum residual disinfectant level could experience stomach discomfort.

Chlorine dioxide (as ClO2)(10049-04-4)

Chlorine dioxide is a water additive used to control microbes and can be used to control tastes and odors. It rapidly disappears from stored water.

Some infants, young children, and fetuses of pregnant women who drink water containing chlorine dioxide in excess of the maximum residual disinfectant level could experience nervous system effects. Some people who drink water containingchlorine dioxide well in excess of the MRDL for many years may experience anemia.

This health effects language is not intended to catalog all possible health effects for disinfectants. Rather, it is intended to inform consumers of some of the possible health effects associated with disinfectants in drinking water when the rule was finalized.

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