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Drinking Water Purification Methods

Ningthoujam Sandhyarani Oct 27, 2018
Water is life for all living beings. Be it plants or animals, potable water is essential for survival. But, water from all sources of water is not safe for consumption. Let's look into the common methods of purifying drinking water.
Drinking water or potable water is water that is supplied for human consumption. The purity of potable water is a major concern throughout the world. It must comply with the scientific standards set for safe consumption, so that people drinking it should not suffer from immediate or long-term health effects.
In short, it should meet the State and Local water quality standards. The United States is known to have one of the purest water supplies in the world. But, in many other countries, people still suffer from acute or chronic illnesses due to drinking of contaminated water.

Necessity of Purifying Drinking Water

Everybody is aware of the fact that about 71% of the earth's surface is covered with water bodies. This balance of water remains fairly constant because of the phenomenon of water cycle. However, we are still struggling for getting sufficient amounts of drinking water. About 1 billion people don't have access to safe drinking water.
This is because, maximum amount of water is present in the oceans (97%) and glaciers (2%). Since ocean water is saline and glaciers are frozen water, they cannot be accessed directly. As for the supplied water, it is often contaminated with pathogens and other dissolved solids, which are harmful.
Water source can broadly divided into surface water and ground water. Rainwater contributes to both. Rainwater, while falling on the earth's surface dissolves gases, suspended particles and other substances. Surface water bodies such as rivers, lakes and reservoirs also have dust particles, microorganisms, minerals and organic matter dissolved in them.
Similarly, ground water contains lots of dissolved minerals. The outcome is that water obtained from these natural sources is not clean, but polluted in one way or the other. Thus, it needs to be treated to meet certain standards before using for consumption.
Based on the source, there are various types of water pollution such as groundwater pollution, surface water pollution and so on. And the effects of water pollution differ based upon the source and the concentration of the contaminants. Let's take a look at the scenario for availability of drinking water to consumers.
While more than 50 percent of the global population get potable water for drinking, the remaining population don't get it. According to the World Health Organization (WHO) report published in 2006, drinking water has been categorized into three, and described in the form of "drinking water ladder".
  • It has been reported that 54% of the world's population use improved drinking water through piped household water connection, which is made available inside the user's dwelling, plot or yard.
  • Around 33% population use improved drinking water sources other than piped water such as public taps or standpipes, tube wells or boreholes, protected dug wells, protected springs and rainwater collection.
  • The remaining 13% population use unimproved drinking water sources such as unprotected well, unprotected spring and surface water (river, dam, lake, pond, stream, canal, irrigation channels).

Common Methods for Purifying Drinking Water

By drinking water purification, we mean the process of removing undesirable biological and chemical contaminants from raw water, so as to make water fit for human consumption. The methodologies for purifying drinking water are totally different from the ones adopted for wastewater treatment.
In addition, water purification is done to meet the standards of chemical, medical and industrial applications. There are both public and private organizations, which deal with water safety and provide useful information, relevant to drinking water issue.
Depending upon the water quality, contaminants present in the water sample and amount to be treated, the methods of purification vary. Say for example, if the sample to be treated is unusual colored or muddy, it should be filtered first through clean cloths, or allowed to settle down for some time.
Then, the actual process of treatment follows. In contrary to this, clear water can be purified directly without the filtration or sedimentation step. So, to get a brief idea about the pollutants that need removal and purification method to be adopted, a water test can be done beforehand. Let's see the various techniques of potable water purification.

Boiling Method

Boiling is the simplest way of purifying water. It disinfects water and kills disease-causing microorganisms such as E. coli, Cryptosporidium and Giardia lamblia, which are commonly present in lakes and rivers.
According to the Wilderness Medical Society, water temperatures above 70 °C kill all pathogens within 30 minutes, and heating above 85 °C disinfects water within a few minutes. It is also observed that water temperature at 100 ºC kills almost all the microbes, including the enteropathogens (pathogens that cause diseases in the intestine).
However, some pathogens such as Clostridium botulinum and their spores get killed only at 118 ºC. To be on the safer side, it is recommended to boil drinking water for a few minutes for drinking.

Filtration Method

Here, contaminants are physically removed using a filter. It gives immediate access to drinking water without adding unpleasant taste. Drinking water filters differ from normal water filters. The size of contaminants getting filtered depends on the pore size of filters, thus the filtrate can be small bacteria (0.3 µm) or the large parasitic cysts (5-30 µm).
The major disadvantage of filtration is that it can't filter virus. It is expensive and even a micro-crack in the medium allows passage of unfiltered water. After filtration, it is always recommended to disinfect by using chemicals or ultraviolet light. Thus, according to many people, water ionizers and reverse osmosis are better options than water filters.

Chemical Treatments

Chemical treatment is an important method of drinking water purification. Over here, water is treated by using chemical halogens in specific amounts, and the most commonly used ones are chlorine and iodine. The effectiveness of this technique depends on the temperature of water, its turbidity, chemical concentration and the contact time.
Note that both chlorine and iodine are not effective against Cyclospora, a diarrhea causing protozoa. Taste of the resulting water is altered after using the chemicals. Flavor kits are available in the market for retaining normal water taste. But, these kits should be added only after the contact time is over, otherwise it will precipitate the halogen.
Chlorine in the form of bleach is used for disinfecting drinking water. The amount of chlorine to be added depends on the concentration. For 5% chlorine concentration, add 2 drops of the same per liter and vice versa. The major drawback with chlorine treatment is the change in flavor. Also, study has found out that chlorine is not effective against Giardia.
As compared to chlorine, iodine is more reliable for disinfecting drinking water. Iodine is available in the form of crystals, tablets and in solution form. It kills almost all the disease-causing microorganisms. The con side is change in taste. It is advised not to use iodine for pregnant women and for those who are allergic to iodine.

Ultraviolet Purification

Ultraviolet water disinfection is the most effective and fast water purification methods. The ultraviolet light inactivates the microbes by destroying their DNA (Deoxyribonucleic Acid), thus preventing the microbes from reproducing. Ultraviolet radiation is effective against all sorts of microorganisms and also, it restores water composition and flavor.
While on the con side, it is applicable only for less turbid water. The more suspended matter water has, the less effective will be ultraviolet purification method. It is because, the foreign particles disturb with the disinfection effect of UV light. Thus, for such a case, filtration or sedimentation should precede water purification.
Other methods are reverse osmosis, using activated carbon filters, water deionizers and distillation. Combined techniques are implemented to get clean water. Drinking bottled water is just an approach to minimize waterborne diseases. Using packaged water is not an actual way of purifying water. It is treated and safe water that is packaged for consumption.
In comparison to raw water that needs further purification, bottled water is ready-to-use water and hence very convenient. But the main drawback is its cost, not everybody can afford buying bottled water. Hence, knowing the ways to purify water and making it safe for drinking is a feasible approach in the long run.

Storage of Drinking Water

Besides adopting correct ways for obtaining potable water, storing pure water in clean containers is a prerequisite. The best choice of containers are food grade plastic or glass bottles with tight-fitting lids. Remember that, there is no use of treating drinking water, if it is kept in dirty containers.
So, wash them with dish soap and hot water on a regular basis. And to disinfect them, a diluted, non-scented household chlorine can be used for rinsing. Never use these storage containers for keeping fruit juices, milk or other liquid foods. Otherwise, the food remains invite bacteria and microbes, which again lead to contamination of water.
It is always better to prevent water pollution, instead of multiple processes for purifying it. Sewage runoff or the municipal waste is the main cause. Household wastes should be disposed to proper waste disposal sites, far away from the water sources. By making such small changes, we can protect the environment as well conserve clean water.