Chlorine is a disinfectant added to drinking water to reduce or eliminate microorganisms, such as bacteria and viruses, which can be present in water supplies. The addition of chlorine to our drinking water greatly reduces the risk of waterborne diseases and is required by the Interior Health Authority.
Chlorine is added as part of the drinking water treatment process. It reacts with all organic matter naturally present in water. This chemical reaction forms a group of chemicals known as disinfection by-products. The most common of these by-products are trihalomethanes (THMs), which include chloroform. The amount of THMs found in drinking water depends on a number of things, including the season and the source of the water.
For example, THM levels are generally lower in winter than in summer, because the amount of natural organic matter is lower and less chlorine is needed to disinfect at colder temperatures. THM levels are also low when wells or large lakes are the drinking water source, and higher when rivers or other surface waters are the source, because they generally contain more organic matter.
Benefits of Chlorine
Current scientific data shows that the benefits of chlorinating our drinking water (less disease) are much greater than any health risks from THMs and other by-products.
Although other disinfectants are available, chlorine remains the choice of water treatment experts. When used with modern water filtration methods, chlorine is effective against virtually all microorganisms. Chlorine is easy to apply and small amounts of the chemical remain in the water as it travels in the distribution system from the treatment plant to the consumer’s tap,This level of effectiveness ensures that microorganisms cannot recontaminate the water after it leaves the treatment plant.
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The TNRD Utility Department analyzes turbidity at each of its water sites every week with a hand-held instrument. As well, all of our water systems constantly monitor turbidity using an online real-time turbidity monitor. The systems generate an alarm and call out automatically if the threshold is exceeded. Notices as outlined by Interior Health Authority’s Turbidity Notification and Education Campaign below are issued to the water customers based on the turbidity levels.
- No Notice: Turbidity below 1 NTU
- Water Quality Advisory: Turbidity 1 – 5 NTU
Used in situations in which the public health threat posed by the water supply system is modest, and actions can be taken to reduce the risks through means other than requiring a Boil Water Notice or Do Not Use Water Notice.
- Boil Water Notice: Turbidity 5 NTU and higher
Used in situations in which the public health threat posed by the water supply system is significant and the nature of the threat is one that can be effectively addressed through boiling of the water.
- Do Not Use: Used in situations where a significant public health threat exists in relation to the water supply system, and the threat cannot be adequately addressed through a Water Quality Advisory or Boil Water Notice.
Turbidity is a water quality term that refers to the relative clarity of water. Turbidity occurs when fine suspended particles of clay, silt, organic and inorganic matter, plankton, and other microscopic organisms are picked up by water as it passes through a watershed. Turbidity levels are typically much higher in water from surface water sources such as streams, rivers, and lakes than from groundwater sources. Some surface water sources exhibit high turbidity levels during periods of high rainfall or snow melt (e.g. spring runoff). Measured in Nephelometric Turbidity Units (NTU), turbidity ranges from less than 1 NTU to more than 1,000 NTU. At 5 NTU water is visibly cloudy; at 25 NTU it is murky.
The Turbidity Index is a messaging tool designed to notify water customers of current turbidity levels and, therefore, the relative risk of drinking the water. The index shows whether water is Good (<1 NTU), Fair (1-5 NTU), or Poor (>5 NTU), and provides specific recommendations for each rating.
Your water supplier will issue a WQA if turbidity levels exceed 1 NTU. Children, the elderly, people with weakened immune systems, and anyone seeking additional protection will be advised to drink boiled water or a safe alternative.
Your water supplier will issue a BWN if turbidity levels exceed 5 NTU. All users will be advised to drink boiled water or a safe alternative.
Turbidity is not so much a health concern as an indicator of health risk. Science has proven that as turbidity increases, the risk for gastrointestinal illness also increases—particularly for at-risk populations such as newborns, the elderly, and people with weakened immune systems (e.g. those with HIV/Aids, undergoing chemotherapy, or taking anti-rejection drugs following a transplant).
Bacteria, viruses, and parasites such as Giardia and Cryptosporidium can attach themselves to the suspended particles in turbid water. These particles then interfere with disinfection by shielding contaminants from the disinfectant (e.g. chlorine).
This question cannot be answered with a simple yes or no. The “safety” of the water fluctuates, and the question at any one time is how safe and for whom. Surface water can contain parasites such as Giardia and Cryptosporidium, which can cause gastrointestinal illness. The Turbidity Index informs people of the current level of turbidity and who should consider drinking boiled water or a safe alternative.
The Province of B.C. recommends that newborns and people with weakened immune systems drink boiled water or a safe alternative at all times if they are served by an unfiltered surface water source. When turbidity levels range from 1-5 NTU, IH and water suppliers recommend that children, the elderly, people with compromised immune systems, and anyone seeking additional protection drink boiled water or a safe alternative. When turbidity levels exceed 5 NTU, IH and water suppliers recommend that all users drink boiled water or a safe alternative.
IH and water suppliers recommend that newborns (up to six months) drink boiled water or a safe alternative at all times. They also suggest that children drink boiled water or a safe alternative if turbidity levels exceed 1 NTU. You can provide them with water that has been boiled for one minute, bottled or distilled water, or water that has been filtered through a well-maintained treatment device.
Water intended for drinking, washing fruits and vegetables, making juice or ice, or brushing teeth should be boiled for one minute. Water should then be refrigerated in a clean, covered container.