Government of Nova Scotia Government of Nova Scotia Nova Scotia, Canada


Drinking Water

Chlorine Disinfection

What is disinfection?

Water treatment is one of the protective steps in making your water safe to drink. Depending on the water source, water treatment can be simple or complicated, however disinfection is always the final critical process of water treatment.

The goal of disinfection is to kill or destroy harmful bacteria and viruses in the water that can cause sickness, disease and even death. An effective disinfectant must also provide residual protection in the water distribution system. Residual protection is the ability to continue to prevent or inhibit the growth of harmful bacteria in the distribution system and the ability to protect against possible contamination that may result from improper cross-connections or main breaks.

Why is chlorine used as a disinfectant?

Chlorine has been shown to be an effective agent against waterborne bacteria and viruses. Chlorine provides residual protection, and is easier and cheaper to use than other disinfection technologies.

Is water with chlorine in it safe to drink?

Yes. Many tests have shown that the amount of chlorine found in treated water is safe to drink. Chlorination of drinking water has virtually eliminated typhoid fever, cholera and many other diseases. It represents one of the greatest achievements of public health protection.

What about THMs?

In some cases, chlorine can react with organic material in the water to form trihalomethanes (THMs). However the potential for their formation can be reduced with the proper treatment technology. Without adequate disinfection of our water supplies, the health risks from micro-organisms would pose a serious immediate health risk.

Are there other disinfectants that could be used?

There are other disinfectants available. Ozone is a powerful disinfectant, however it does not maintain a good residual in the distribution system and the technology is more complex than chlorination. Ultraviolet light is a good disinfectant and is easy to maintain, but provides no residual. Chloramines, a mixture of chlorine and ammonia, provide a stable residual in the distribution system, but they do not have the disinfecting power of chlorine. Chlorine dioxide is a powerful disinfectant and can maintain a residual, however the technology is relatively new and complex.

Why do I smell and taste chlorine when I didn't before?

Nova Scotia Environment is taking the safety of drinking water very seriously. The Nova Scotia Guidelines for Monitoring Public Drinking Water Supplies require that where a chlorine disinfection system is being used, a minimum free chlorine residual of 0.2 mg/L should be measured at all points in the water distribution system and must not exceed 4 mg/L at any time. For some water utilities this may have resulted in having to increase the amount of chlorine being added to the water at the treatment plant beyond what was added in the past.

Before they added chlorine, my water looked, smelled and tasted better.

Even though water may look, smell and taste okay, this does not guarantee that the water is safe because the chemicals and microbes that could make you sick cannot be seen, smelled or tasted.

I don't like the taste of chlorine in my water. What can I do?

Chlorine can impart a taste to the water that some people may not like. This taste does not mean the water is not safe to drink; in fact it is an indication that your water is being properly treated.

Storing water in an uncovered glass container in the fridge overnight will allow the chlorine in the water to dissipate. As well, activated carbon or charcoal filters can remove the background taste of chlorine. It is important to remember that the disinfectant has been removed and the water must be treated like any other food. Keep it covered and use it as quickly as possible.