Public awareness of the potential for groundwater and surface water contamination and the growing interest in outdoor recreational activities in areas not serviced with safe drinking water have led to increased usage of water disinfection devices.
In Canada, over four million people depend on private wells for their drinking water. In addition, lakes, rivers and other sources of surface water often serve as the sole water supply for cottagers, campers, boaters and hikers. Unlike municipal water systems, these water supplies may not be subjected to routine testing for microbiological contamination or to appropriate disinfection procedures.
Private wells can become contaminated if they have been poorly constructed or improperly sited or if they have been infiltrated by contaminated surface water. In fact, the aquifer (the water-bearing underground layer of porous rock or sand) itself can even be the source of contamination. Surface waters and unprotected groundwaters are susceptible to faecal contamination from humans, livestock, wild animals and even house pets.
Water taken from lakes, rivers, streams and ponds may look clean and have no undesirable odour or taste. Unfortunately, however, pathogens found in water not only are harmful, but also are invisible to the naked eye and may be odourless and tasteless. These bacteria, viruses and protozoa can cause mild nausea and fever or can develop into more serious illnesses, such as severe diarrhoea, hepatitis or typhoid fever. Water from lakes, rivers, streams and ponds should always be disinfected before being used for drinking or cooking.
Microbiological contamination is the primary cause of disease outbreaks associated with drinking water. Between 1974 and 1996, over 160 waterborne disease outbreaks involving some 8000 people were reported in Canada. It is estimated that only 10 per cent of all waterborne outbreaks occurring in Canada are ever reported.
Depending on the source of the water, conditions of use, and magnitude and extent of microbiological contamination, disinfection may be needed occasionally over short periods of time or on a continuous basis.
For occasional, emergency or short-term disinfection, there are several simple methods that do not require special devices:
Protozoan cysts are often present in surface waters. Because cysts are more resistant than bacteria and viruses, iodine and chlorine should not be relied upon to inactivate them. When water must be continuously disinfected because of the unacceptable quality of the supply, the possibility of sporadic contamination or the presence of cysts, a water treatment device incorporating filtration and disinfection should be used rather than short-term disinfection methods.
Water treatment devices can be divided into two groups, according to function. There are several types of devices within these two groups, each suited to a specific water quality problem. Water treatment devices that disinfect water will be discussed here. Those that improve the overall taste, smell and appearance of the water or remove undesirable chemicals and minerals are discussed in the Health Canada "It's Your Health" publication entitled Water Treatment Devices for the Removal of Taste, Odour and Chemicals.
Point-of-use devices are portable, plumbed-in or faucet-mounted and are used to treat the water at a single tap or multiple taps for drinking and cooking only. Point-of-entry devices are installed on the main water supply and treat all the water entering the home.
Chlorinators, iodinators and ultraviolet light (UV) devices are most practical when it is necessary to disinfect water that serves a whole dwelling. Chlorine and iodine kill most disease-causing organisms and require short to moderate contact times. In fact, the use of chlorine on municipally treated water systems has virtually eliminated waterborne infectious diseases such as typhoid and cholera. Chlorine or iodine treatment alone, however, may not provide adequate protection against protozoa such as Giardia lamblia and Cryptosporidium parvum. If protozoa are present or suspected, it is recommended that the water be first passed through a filter with a 0.1-micrometre or smaller pore size to remove these parasites and then chemically treated with chlorine or iodine to kill bacteria and viruses.
Iodine disinfection of drinking water, however, should be reserved for emergency and occasional use (e.g., at a weekend cottage or in recreational vehicles). Iodine should not be used for long-term continuous disinfection because it is physiologically active, and ingestion in excessive amounts may be harmful.
UV devices are also effective against bacteria, viruses and protozoa, add nothing to water and produce no taste or odour; in addition, only a few seconds' exposure to UV light is required if the water is clear. They do not, however, ensure the safety of the water beyond the point of application, so that flushing of the system is recommended after periods of non-use. Point-of-use UV light devices are also available. A pre-filter, however, should always be employed to reduce turbidity, thus improving the effectiveness of the UV light.
Ceramic or glass fibre filters handle smaller amounts of water and are useful when water from just one tap is to be treated for drinking and cooking or to provide drinking water while camping, boating or hiking. Such filters can remove bacteria and protozoa from mildly contaminated waters. However, they are not suitable for removing viruses or for treating highly contaminated water. Therefore, when treating surface waters, it is recommended that these filters be used in conjunction with disinfection. Portable glass fibre or ceramic filters with iodine- releasing resins are available to disinfect water for campers, etc., or for travellers in countries where the safety of the drinking water is questionable. Some iodine-releasing devices contain an activated carbon filter to remove excess iodine from the water.
Distillers and ozonators are point-of-use devices suitable where electric power is available, and where there is sufficient space to install the equipment. Distillation is commonly used to reduce the levels of all chemicals in drinking water. These distillation devices are effective for the removal of inorganic chemicals, including heavy metals, and some organic chemicals, but are often combined with activated carbon for the removal of certain "volatile" chemicals (e.g., trihalomethanes, tetrachloroethylene). The boiling process also kills any microorganisms (viruses, bacteria and protozoa) present in the water. There are no known beneficial or harmful health effects associated with the ingestion of demineralized or distilled water.
Ozonators produce small quantities of ozone, a strong oxidizing agent that is effective in killing pathogens over a short period of time. Ozonation produces no taste or odour in the water. The process is dependent, however, on good mixing of ozone with the water. Unlike chlorine and iodine, ozone does not protect the water after application. Ozonation is often combined with activated carbon filtration to achieve more complete water treatment.
When camping, canoeing or hiking, you should assume that all waters contain disease- causing organisms, and you should disinfect the drinking water before use. Care must also be taken to avoid ingestion of untreated water during other activities (for instance, when brushing your teeth).
Wells should be analysed routinely for microbiological contamination. According to Health Canada's Guidelines for Canadian Drinking Water Quality (Sixth Edition, 1996), no sample should contain more than 10 total coliform bacteria per 100 mL, and none of the coliform bacteria should be Escherichia coli or faecal coliforms. If well water does not comply with this guideline, it should be disinfected using one of the methods described above.
As most disinfection systems require clear water to ensure maximum efficiency, it may be necessary to combine two specific devices - one to remove various organic or inorganic compounds or to reduce turbidity in the water, and one to reduce microbiological contamination.
Ultimately, the best approach to ensure complete disinfection of water intended for human use and consumption is a multi-barrier one, consisting of collecting water from the cleanest source possible, followed by filtration and disinfection.