Her Majesty the Queen in Right of Canada,
represented by the Minister of Health Canada
HC Pub.: 3581
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To avoid the risk of people becoming sick (diarrhoea, abdominal cramps), it is necessary to treat source water (including surface water from lakes and rivers or from underground waters) before it reaches the taps in people's homes. Disinfection is one of the most important steps in water treatment because it kills unwanted microorganisms. Most commonly, water treatment plants use two steps in the disinfection process: primary disinfection and secondary disinfection.
Primary disinfection is the first disinfection step that takes place inside the water treatment plant. It kills unwanted microorganisms that are present in the source water.
The choice of disinfectant is based on the quality of the source water and treatment needs. Chlorine is the most commonly used and most effective disinfectant.
Secondary disinfection is the second disinfection step to protect the water in the water pipes and water reservoir (the distribution system). Although microorganisms are killed during primary disinfection, if the distribution system is not cleaned regularly, or if a pipe breaks, recontamination can occur.
During secondary disinfection, a certain amount of disinfectant, called the disinfectant residual, must remain in the distribution system all the way to the very last consumer (end user of the pipe system) to ensure that all consumers receive safe drinking water.
Chlorine is the most commonly used disinfectant. It has been used to disinfect water and make it suitable for drinking for the past 100 years.
A concern with the use of chlorine as a disinfectant is its ability to react with organic matter (such as leaves) that is present naturally in surface water. If organic matter is not removed, it combines with chlorine, producing unwanted compounds known as disinfection by-products (DBPs). To avoid this situation, water treatment plants usually remove organic matter as a first step. It should be noted that the possible harmful effects of DBPs are minor compared with the harmful effects that may result from drinking water that has not been disinfected.
The taste and odour of chlorine in drinking water can be another concern for consumers. However, chlorine makes water safe to drink, and there are simple home remedies that can be used to improve its taste.
The simplest way to improve the taste of chlorinated water is to let the water stand for a few hours. Chlorine will evaporate in about a day if the water is exposed to circulating air and sunlight. If the water is refrigerated, it will take about two days for the chlorine to evaporate.
A quicker way of reducing chlorine smell from tap water is to add fruits or vegetables such as oranges, lemons, limes and cucumbers, or to dissolve a crushed Vitamin C tablet to the water. This should remove most of the chlorine in about an hour.
There are no risk associated with the taste and the odour of chlorine in drinking water.
Home carbon filters are available for those who find the taste and odour (or the aesthetic effects) caused by chlorine to be too strong. Filters should be certified as per the NSF International/American National Standards Institute Standard 42. It is crucial to regularly replace the filter as recommended by its manufacturer. If this is not done, it could cause the water to become contaminated.