Dispatch No. 60 - Health and Welfare Canada Publication
Point-of-use Water Treatment Devices
Canadians are becoming concerned about the quality of their drinking water due to an increased awareness of environmental pollution and of the limitations of water treatment processes. Safe drinking water is essential to health. Unfortunately, many cities are located close to sources of pollution and thus some Canadians fear for the chemical quality and safety of their drinking water.
Chemically "pure" water does not exist in nature; water is known as the universal solvent and always contains a variety of chemicals and minerals. The presence of these substances does not mean that water is not "safe," but to many people, the mere mention of chemicals in water brings to mind thoughts of pollution, disease and cancer.
A visible manifestation of the public's concern is the phenomenal rise in the sale of point-of-use water treatment devices. Current sales are at about 100 000 units annually, with a retail value of $20 million.
About 70% of the treatment devices sold use activated carbon filters. Health professionals are concerned because bacteria tend to grow in carbon filters over time, which means that some water treatment devices may actually contaminate the water they are intended to treat.
Health Protection Branch
It is due to the burgeoning use and concomitant questions about safety and effectiveness of water treatment devices, that the Environmental Health Directorate of the Health Protection Branch, Health and Welfare Canada, has established a program to evaluate these devices. At present, such devices are not subject to regulation and there are no accepted performance standards: In general, it is considered essential that the water treated by point-of-use devices meet the quality specified in the Guidelines for Canadian Drinking Water Quality.
In Canada, provision and monitoring of most drinking water is a provincial responsibility. However, the general provisions of the federal Health and Welfare Act (Section 5) provide the basis for any research or regulatory activities carried out. For example, Canada's guidelines on drinking water quality have been revised, to take into account new scientific data and concerns since the last revision.
Water treatment devices can be classified into two groups: those used for the disinfection of water, and those which remove taste, odour and chemicals.
Disinfection of water may be required on a continuous basis or for occasional use when microbial contamination of water may have occurred. For occasional or short term use, there are several simple methods of disinfecting water which require no devices:
1. boiling water for one minute will kill most common pathogens, but boiling for at least five minutes will ensure disinfection;
2. household bleach, which contains four to five percent sodium hypochlorite, will disinfect water when at least five drops are added to four litres of water and left to stand for 30 minutes;
3. water purification tablets which release chlorine or iodine may be purchased and are especially useful for travelers when used according to manufacturers' directions.
Where disinfection of water must be carried out on a continuous basis due to dubious quality of raw water or the possibility of periodic contamination, a point of use device may be more practical than the short term methods described. Efficacy, reliability, cost and maintenance requirements are all important considerations; for a review of the systems used successfully in Canada, see Table 1.
For disinfection of water serving a whole house, chlorinators and ultraviolet light devices are the most practical. Chlorine generally kills disease-causing organisms and requires short to moderate contact time, depending on the amount of organic matter present. Chlorinators are widely used in large municipal systems as well as on small private systems such as wells.
(Note from H2O 1997: follow on de-chlorinators and point of use systems are very popular to remove the chlorine, other organic chemicals and particulate such as silt, asbestos or the dead organisms)
Ultraviolet devices are also effective against pathogens, add nothing to water, produce no taste or odour, and in clean water require only a few seconds of exposure to be effective. The drawback is that they do not ensure safety of water beyond the point of application so that flushing of the system is recommended after periods of non-use.
Ceramic candles and iodinators handle smaller amounts of water and are useful when the water from just one tap is to be treated for drinking and cooking. Care should be taken in these cases to avoid ingestion of untreated water by using water from other taps for brushing teeth, etc. Ceramic cartridge filters consist of a cylindrical element or "candle" with a hollow centre. Water is filtered from the outside of the ceramic to the inside, and bacteria and particulate matter are filtered through the candle pores. The candle usually contains silver which helps prevent bacterial growth into the centre. Occasional abrasion of the candle surface is required to remove material and to restore normal flow rate.
(Note from H2O 1997: Whole house and commercial high flow rate candles are now available)
Iodinators are relatively simple devices which disinfect water by dosing an iodine solution into the main water stream. Iodine should not be used, however, for long-term continuous disinfection because the element is physiologically active and an excessive intake may be harmful.
Distillation and ozonation are suitable for use where electric power is available and there is enough space to house the apparatus. Water is boiled in a still and the vapour is condensed and collected. The process removes most metals and inorganic contaminants but it may not remove all organic materials. Thus, stills may be combined with carbon filtration to achieve more complete water treatment. Ozonators produce small quantities of ozone, a strong oxidizing gas, which is effective in killing pathogens in a short exposure time, while producing no taste or odour. The process is dependent on good mixing of ozone with the water however, and the residual effect is very short-lived.
Removal of Chemical Contaminants
It is not generally appreciated that much of Canada's drinking water is highly processed. In fact, more than a million tons of chemicals are added each year to drinking water. Despite the fact that most municipally treated water is adequately processed, many Canadians fear the presence of harmful contaminants. It is true, too, that the chlorination of drinking water may produce low levels of halogenated by-products some of which are suspected carcinogens. This fact has spurred interest in alternative methods of water treatment. In most cases, no health risk is present, but certain aspects of the water supply in some areas may not be esthetically appealing.
A number of devices are available for removing chemicals and improving the quality of water (see Table 2). The most common type is the water softener; its main function is to remove calcium and magnesium from "hard" water. While softening water makes it more suitable for washing and prevents deposits in appliances and pipes, the water is not generally recommended for drinking or cooking due to its increased sodium content, decreased essential mineral content and the potential of bacterial growth.
Carbon filters (powdered, granular or pressed block) are more effective in removing organic chemicals from water than inorganic; they are often used to remove taste, odour, chlorine and hydrogen sulphide and may be combined with other treatment processes. Nevertheless some pressed carbon block filters will reduce levels of heavy metals in water.
The principal disadvantage of activated carbon filters (including those which contain silver) is their ability to foster bacterial growth on the trapped organic substances, and to release those bacteria into the water. Some carbon filters contain membrane filters to retain the bacteria, but these membranes will not remove all microorganisms. It is imperative then that all activated carbon filters be used only on water which meets guidelines for microbiological safety, and that these filters be flushed before use.
Another disadvantage is the variability in removing organic contaminants from water. Research has indicated as well that the efficiency of these filters with regard to some contaminants decreases with use.
The risk of using activated carbon filters can be lowered by following these steps:
1. Use only with microbiologically safe water.
2. Flush for at least 30 seconds before use.
3. Change filters frequently.
4. Follow manufacturers' advice for installation and service.
As already mentioned, both distillation and reverse osmosis processes remove chemical contaminants such as heavy metals, but they are not totally effective against organic contaminants. In addition, reverse osmosis membranes are not highly efficient at water pressures normally encountered.
Storage of Water
Ideally, treated water should be consumed immediately after treatment to prevent deterioration. Some types of bacteria can grow in almost any water, especially at warm temperatures. If water is not to be used right away, it may be stored for no more than a few days in the refrigerator. Home treatment devices should be flushed for 30 seconds after any period of non-use. Water that is stored in tanks at room temperatures -- in boats and campers, for example -- poses a special problem. Storage tanks should be cleaned and disinfected periodically, and the water replaced; disinfection of the water may be necessary to ensure safety.
Choosing a Water Treatment Device
Advertising claims for a given point-of-use water treatment device are an important factor in the selection of a device by most consumers. For this reason, it is essential that claims accurately represent the performance of the product. Tests of such a device carried out for the manufacturer by reputable laboratories can be useful in evaluating the claims made for it. Often, however, these tests may be incomplete or insufficiently described to be useful. If there is any doubt about the effectiveness of the device, advice should be sought from provincial health or environment officials who are the experts in this field.
In conclusion, it is important for health professionals advising consumers about the safety and effectiveness of point-of-use water treatment devices to understand the following points:
1. The specific contaminant in the water supply must be known in order to choose the most effective treatment process.
2. Most point-of-use devices are intended for use only on municipally treated water, not "raw" untreated water.
3. Activated carbon filters can pose a significant risk to health if installed or used improperly.
Table 1. Devices for Disinfection of Water
|May not be effective against viruses
|May require additional filters to remove protozoan cysts
|Residual test kit, electricity
|Effective against all pathogens
|Batch system - water may not be available when required
|May require additional filters to remove cysts. Possible physiological effects of iodine
|Residual test kit
|Low operating cost
|May require additional filters to remove cysts. Iron, suphur and manganese must not be excessive
|Uses no chemicals
|May require additional filters to remove cysts. May be only partially effective if water is turbid
|Electricity, UV monitor
Table 2. Devices for Taste, Odour and Chemical Removal
|Removes taste, odour, organics, chlorine, low levels of hydrogen sulphide
|Should be used on microbiologically sage water
|Cartridges should be changed regularly
|Iron, manganese, hydrogen sulphide removal
|Quantity used must be accurate
|Electricity, filter to remove precipitates
|Removes inorganic salts, some organic chemicals, particles, hydrogen sulphide
|May concentrate some organic chemicals
|Iron, manganese, hydrogen sulphide removal
|May clog or reduce effectiveness due to bacterial growth
|Backwash and regenerate regularly, replace media
|Turbidity, particle removal
|May clog or reduce effectiveness due to bacterial growth
|Regular changing / cleaning
|Inorganic salts removal
|Susceptible to clogging
|Adequate water pressure, flushing
|Hardness (calcium, magnesium) removal
|Elevates sodium content; possible bacteria growth
|Usually require electricity
"Critical Issues in Drinking Water Quality". Proceedings of National Conference on Critical Issues in Drinking Water Quality. Health and Welfare Canada/Federation of Associations on the Canadian Environment. Ottawa, February 1984.
Canadian Water and Wastewater Association
24 Clarence St. West
Environmental Health Directorate publications:
77-EHD-8 - Survey and test protocols for point-of-use water purifiers
79-EHD-33 - Laboratory testing of point-of-use ultraviolet drinking water purifiers
80-EHD-46 - Laboratory testing and evaluation of iodine- releasing point-of-use water treatment devices
80-EHD-54 - Assessing the effectiveness of small filtration systems for point-of-use disinfection of drinking water supplies.
Environmental Health Directorate
Health Protection Branch
Health and Welfare Canada. Guidelines for Canadian Drinking Water Quality, 1987.
Canadian Government Publishing Centre
Supply and Services Canada
Publicity and Promotion Section
Cat. No. H48-10/1987E. Cost: $2.50
Tobin, R.S. Water Treatment for the Home or Cottage.
Canadian Journal of Public Health. Vol. 75, pp. 79-82,
Tobin, R.S. Testing and Evaluating Point-of-Use Treatment
Devices in Canada. Journal of the American Water Works
Association. Vol. 79, pp. 42-45, Oct. 1987.
Published by authority of the Minister of National Health and Welfare
© Minister of Supply and Services Canada 1989
Cat. No.: H49-46/8-1990E
Dispatch No. 60
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