Removal of Taste, Odour and Chemicals

Canadians are becoming increasingly concerned about environmental pollution and the limitations of water treatment processes. Because safe drinking water is essential to human health, the chemical and biological quality of our drinking water are of great importance.

Although the presence of chemicals in our drinking water often creates concern about pollution and disease, chemically pure water does not in fact exist in nature. Water, which is known as the universal solvent, always contains a variety of chemicals and minerals. Fortunately, Canadian drinking water supplies are largely free of the disease­causing organisms found in water supplies of many developing countries.

Even so, water treatment devices have become common household appliances in recent years. It is estimated that as many as 100 000 units are sold annually in Canada. These water treatment systems tend to be regarded as something between a device that will protect health from a perceived risk and an everyday kitchen appliance that can improve the appearance, taste and smell of our drinking water.

Types of Devices

Water treatment devices can be divided into two groups, according to function. Those that improve the overall taste, smell and appearance of the water or remove undesirable chemicals and minerals will be discussed here. Those that disinfect contaminated water are discussed in the Health Protection Branch Issues paper ­ Water Treatment Devices ­ For Microbiological Purification.

Point­of­use devices are treatment systems installed on single or multiple taps and are intended to treat water for drinking and cooking only. Point­of­entry devices are installed on the main water supply and treat all the water entering the home.

Several types of devices are used to improve the aesthetic qualities of drinking water and to remove chemicals. Those that employ an activated carbon filter are the most common, and are usually installed at the point of use. Activated carbon filters are generally more effective in removing organic chemicals. They are often used to improve taste, smell and appearance and are frequently combined with other treatment processes to provide a more complete water treatment system.

A number of other point­of­use devices are employed primarily for removing undesirable chemicals from drinking water. Processes employed include reverse osmosis, absorption, ion exchange, and distillation.

A reverse osmosis treatment system usually consists of a semi­permeable membrane, water storage tank and dispensing faucet. This system can remove inorganic chemicals and is often combined with an activated carbon filter to remove chlorine and organic chemicals.

Filters containing activated aluminum oxide have recently appeared on the market. These devices are used to remove heavy metals, particularly lead from drinking water.

Various pitcher­type products are also available. In addition to having activated carbon filters, these devices may include an ion­exchange resin for the removal of inorganic chemicals responsible for “hard” water.

Distillation systems are commonly used to reduce the levels of all chemicals in drinking water. These systems boil water in one compartment and condense the vapour and collect it in another. Distillation systems are effective for the removal of both organic and inorganic chemicals but are often combined with activated carbon for the removal of certain “volatile” chemicals (e.g. Trihalomethanes, tetrachloroethylene). There are no known beneficial, nor harmful health effects associated with the ingestion of demineralized or distilled water.

Two widely used point­of­entry water treatment devices are water softeners andgreensand filters. These are commonly used in rural areas. Water softeners reduce water hardness but do not remove organic chemicals. Greensand filters are designed primarily to remove iron, manganese and hydrogen sulfide from water.

Potential Health Problems Associated with the Use of Water Treatment Devices

The activated carbon filters used in many water treatment devices can, in themselves, become a source of contamination. Over time, the filter can become saturated with chemical contaminants, resulting in the release of these compounds into the finished water, possibly in even higher concentrations than in the source water. As well, build up of organic matter on the filter can lead to bacterial growth over even short periods of time, i.e., overnight. Some manufacturers have devised various methods of reducing the microbial growth, such as adding silver, but the effectiveness of these methods is questionable.

Although softened water is more suitable for washing and helps prevent deposits in appliances and pipes, it is not generally recommended for drinking and cooking due to its increased sodium content, decreased essential mineral content and the potential for bacterial growth. Bacterial growth may also occur in greensand filters. A variety of salt­free water softeners and conditioners have appeared on the market. Although the use of these devices does not appear to present a health hazard, there is some controversy over their effectiveness.

What the Consumer Can Do

The health risks associated using a water treatment device employing an activated carbon filter can be reduced by following these steps:

  1. use only on municipally­treated or other water supplies known to be free of microbial contaminants);
  2. flush for at least 30 seconds before each use and
  3. change filters or units (if unit is disposable) frequently;
  4. carefully follow the manufacturer’s instructions for installation and service.

Water not consumed immediately after point­of­use treatment should always be stored in the refrigerator to avoid microbial contamination.


Although there is currently no specific legislation governing water treatment devices, Health Canada considers it essential that water processed through a water treatment device meets the quality set in the Guidelines for Canadian Drinking Water Quality(Health Canada, 5th Edition, 1993). It is worthwhile to note that water already satisfying the criteria in he guidelines does not normally require additional treatment in the home, at least for health­related reasons.

Health Canada insists that activated carbon filters and related packaging, promotional and instructional materials be clearly labelled “Use only on municipally treated water or other supply known to be microbiologically safe”. This agrees with the voluntary guidelines developed by the Canadian Water Quality Association for the advertising and promotion of activated carbon filters.

In addition, Health Canada has worked closely with the National Sanitation Foundation(NSF) International to develop performance standards for water treatment devices. The Department encourages manufacturers to seek certification of their products against the NSF International standards. These standards and the NSF International listing are now widely accepted in North America as evidence of specific performance, by brand and model, for removal of specific contaminants, as well as mechanical integrity of the devices.

Ultimately, compliance with these voluntary performance standards should make the selection of an appropriate device much easier for the Canadian consumer.