Frequently Asked Questions (FAQs)

Q: What are the main uses of chlorine in Canada?
A: Chlorine is predominantly used inCanada for drinking water disinfection, pool & spa disinfection, and surface disinfection, particularly for food preparation.

Drinking Water Disinfection

Q: Why is chlorine added to drinking water?
A: Chlorine destroys disease-causing germs and helps make water safe to drink. Waterborne diseases once killed thousands of North American every year. Following its first use in Jersey City, New Jersey in 1908, drinking water chlorination started in Canada, in Ottawa, in 1909 before its rapid spread throughout North America helped to virtually eliminate waterborne diseases like cholera and typhoid fever. Drinking water chlorination played a major role in increasing North Americans’ life expectancy by 50 percent during the 20th century.

Besides killing dangerous germs like bacteria, viruses and parasites, chlorine helps reduce disagreeable tastes and odors in water. Chlorine also helps eliminate slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks. In its Guidelines for Canadian Drinking Water Quality – Chlorine Guideline Technical Document Health Canada says “The majority of drinking water treatment plants in Canada use some form of chlorine to disinfect drinking water: to treat the water directly in the treatment plant and/or to maintain a chlorine residual in the distribution system to prevent bacterial regrowth.”

Q: How does chlorine destroy germs in drinking water?
A: Chlorine destroys waterborne germs by penetrating their slime coatings, cell walls and resistant shells. Chlorine either kills the germs or renders them incapable of reproducing.

Chlorine is highly effective against most disease-causing germs found in drinking water sources.

The ability of chlorine to kill germs depends on both the concentration of chlorine in the water and the amount of time that the chlorine has to react with microorganisms (contact time). While chlorine quickly kills most waterborne germs, a few microorganisms, such as Cryptosporidium, are resistant to typical chlorination practices. Therefore, some water systems may require additional treatment steps to protect against particularly resistant pathogens.

Q: Is chlorine in drinking water safe?
A: The small amount of chlorine added to disinfect drinking water is safe for consumption. According to the Health Canada Guidelines for Canadian Drinking Water Quality – Chlorine Guideline Technical Document, the Federal-Provincial-Territorial Committee on Drinking Water has deemed that there is no need to establish a guideline for chlorine in drinking water: “It is not considered necessary to establish a guideline for chlorine in drinking water, based on its low toxicity at concentrations found in drinking water as a result of treatment. Any measures taken to limit the concentration of chlorine or its by-products in drinking water supplies must not compromise the effectiveness of disinfection.”

Q: What are disinfection byproducts?
A: Disinfection byproducts, or DBPs, are chemical compounds formed unintentionally when chlorine or other disinfectants react with natural organic matter in water.

According to the Health Canada Guidelines for Canadian Drinking Water Quality – Chlorine Guideline Technical Document “Some of the natural organic matter in the treated water has the potential to react with chlorine to form CDBPs at the plant and within the distribution system. The types and structures of CDBPs are complex and are a function of water quality and treatment conditions (IPCS, 2000). The most common CDBPs present in chlorinated waters include trihalomethanes (THMs) and halogenated acetic acids (HAAs). Because elevated levels of CDBPs may have adverse effects on health (WHO, 1995; U.S. EPA, 1999a; Health Canada, 2000; IPCS, 2000), every effort should be made to maintain their concentrations as low as reasonably achievable, without compromising the effectiveness of disinfection. This can be done using strategies such as precursor control and removal or application of alternative/modified disinfection practices (IPCS, 2000), including optimization of the treatment process.”

While DBPs should be reduced where possible, protection from germs remains the top priority. The World Health Organization strongly cautions that “The risk of illness and death resulting from exposure to pathogens in drinking water is very much greater than the risks from disinfectants and DBPs…Efficient disinfection must never be compromised.”

Pool & Spa Disinfection

Q: Why is chlorine added to swimming pools and spas?
A: Chlorine kills harmful microorganisms that can cause health-related problems in swimming pools and spas. Chlorine-based swimming pool and spa disinfectants help prevent swimmers’ ear, athlete’s foot, skin rashes and diarrhea. Legionnaires’ Disease and Pontiac Fever can also be prevented with proper chlorination, particularly in the hot tub and spa environment. The U.S. Centers for Disease Control and Prevention (CDC) calls chlorine and proper pH, “the first defense against germs that can make swimmers sick.”

Q: What are the advantages of using chlorine to disinfect pools?
A: Chlorine is the disinfectant of choice for the majority of public and residential pools in Canada. Chlorine levels are easy to monitor and can be adjusted based on pool conditions such as the number of swimmers in a pool. A major advantage is that chlorine provides a residual level that continues to protect long after it is applied. Disinfectants such as ozone and ultraviolet light can provide supplemental treatment to control chlorine resistant germs like Cryptosporidium. However, none of these technologies eliminates the need to maintain a proper chlorine levels in pool water.

Q: Why do some pools seem to use too much chlorine?
A: Swimmers often mistakenly blame red eyes, itchy skin and a strong chemical smell of pool water on “too much chlorine.” Generally, the odour and irritation they notice is not due to chlorine, but to chloramines, chemical compounds that build up in pool water when it is improperly treated. A properly managed pool has little odour.

Chloramines form when chlorine combines with ammonia and other compounds found in perspiration, urine, saliva, body oils and lotions that are brought into pools on the bodies of swimmers. Swimmers can help prevent chloramines forming in pools by showering before swimming. Pool managers can closely monitor and adjust pool chemical levels to minimize chloramines formation.

Unhealthy levels of chloramines can be treated with a high dose of chlorine, known as shock treatment. Shock dosing—conducted when swimmers are absent from the pool—destroys chloramines, organic contaminants, and a variety of germs.

Q: Is swimming in an indoor pool unhealthy?
A: Medical experts agree that swimming is a healthy form of exercise for children and adults. For indoor pools, in addition to appropriate chemical treatment, proper ventilation is important to avoid the build-up of compounds like chloramines. Always use your senses to check for the signs of a healthy pool.

Surface Disinfection

Q: How can I use chlorine bleach to disinfect surfaces in my home?
A: A chlorine bleach solution can be used as a handy, inexpensive household disinfectant. It can be applied in the kitchen to food preparation surfaces, like countertops and cutting boards, to destroy foodborne germs like e.coli and salmonella. Bathroom surfaces may be sanitized using chlorine bleach, as can hard surfaces in the sick room. During flu season, disinfecting commonly touched surfaces, such as door knobs and dials, with chlorine bleach solution can help prevent the spread of the flu virus among family members.

To use chlorine bleach for general surface disinfection, first wash the surface with hot, soapy water to clean. Thoroughly rinse off soap. Disinfect by applying a fresh mixture of 1 tablespoon (15 mL) of household bleach in one gallon (1 US Gallon = 3.78 L) of cool water. Allow to air dry.

Download disinfection posters and order a free consumer kitchen magnet.

Always read and follow instructions on the labels of bleach containers and other household cleaners. Click here for more tips help ensure that you are handling and using your chlorinated household products safely.

Q: Is using bleach or other chlorine disinfectants bad for the environment?
A: Handled properly, consumers can safely use bleach without significant environmental effects. As it reacts with germs and stains, between 95 and 98 percent of it chlorine bleach breaks down and turns back into salt water. Importantly, waste water treatment facilities use chlorine disinfectants to destroy oxygen-robbing contaminants in wastewater, helping to preserve the quality of our nation’s rivers and streams into which the treated wastewater is discharged.

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