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Common Methods of Water Disinfection

Table of Contents
  1. Boiling
  2. Distillation
  3. Chemical Water Disinfection
  4. UV Water Purification
  5. Filtration

Drinking water disinfection is routine in developed countries with adequate sanitation and safe hygiene practices. Depending on the source of the water, municipal water treatment plants use a variety of physical and chemical water disinfecting techniques before the water reaches your sink at home. The most common methods of water purification include heat, distillation, chemical treatment, UV light and filtration. In developing countries, where residents don't have access to safe sanitation and hygiene, alternative methods are often used. In emergency situations, it is good to familiarize yourself with the various techniques used so that you can disinfect the water yourself, should the need arise.

Boiling


Waterborne illness is caused by bacteria, viruses and parasitic cysts - Giardia and Cryptosporidium - often found in rivers, lakes and other dirty water sources. Heating the water to boiling point kills these disease-causing microorganisms and is the surest way to make contaminated water safe for drinking. The Centers for Disease Control (CDC) and the Environmental Protection Agency (EPA) both recommend that you boil water vigorously for one minute, to ensure that all microorganisms are killed. At altitudes higher than one mile, boiling point decreases, so you should boil the water for at least three minutes. Boiling will not rid the water of any unpleasant taste. However, aeration of the water may improve bad taste. To aerate, pour the water back and forth from one container to another and allow it to sit for a few hours, or add a pinch of salt for each liter or quart of water boiled. In developed countries, boiling is usually the recommended solution in emergency situations where accidental water contamination has been reported. However, if boiling is not an option, residents often resort to drinking bottled water.

Distillation


Distillation is the process of boiling water to produce water vapor which then condenses onto a cool surface. The solutes do not normally vaporize and are left in the boiling solution leaving the condensed water vapor almost completely pure. However, it is possible to get water that is not completely pure at the end of this process, due to contaminants with similar boiling points and unvaporized droplets being carried with the steam. Distillation is a controversial water disinfecting method, because it de-mineralizes the water, leaving it void of essential minerals like magnesium and calcium, which prevent nutritional deficiency. It also increases the risk of toxic poisoning, as it more readily leaches metals like lead from household piping.

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Chemical Water Disinfection


Two of the most common chemical water disinfecting agents, which may be used in an emergency situations, are chlorine and iodine (halogens). Chloramines and Ozone are also used by water treatment plants. In order for chemical disinfection to be effective, the water must be filtered and settled first. Chemical disinfection often leaves an undesirable taste in water, which an activated carbon filter can remove post-treatment. Otherwise, you can minimize bad taste and odor by reducing the disinfectant concentration and increasing contact time before drinking. Another option to remove the taste of chlorine and iodine from water is to add a pinch of ascorbic acid, which is available in crystal or power form. This converts chlorine into chloride and iodine into iodide, both of which have no taste or odor.

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UV Water Purification


Ultraviolet radiation penetrates the cell walls of microorganisms and disrupts their DNA, making them unable to reproduce. Though they remain present in the water, they are inactive, and thus, leave no risk of waterborne illness. UV light is effective against viruses and bacteria but may not inactivate parasitic cysts. As with ozone, a secondary method is often necessary to prevent the regrowth of organisms, post-treatment.

Filtration


Filtration is often the first and last step taken in these common methods of water disinfection. It is recommended prior to the disinfection of water to remove particles that hinder the disinfecting process. Following disinfection, filtration may also be used as a secondary method to remove cysts, along with the bad taste and odor caused by chemical byproducts.


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