Drinking Water Purification Methods

Drinking water or potable water is water that is supplied for human consumption. It has been a major concern throughout the world. Drinking water must comply with the scientific standards that would enable it safe for the consumption without risk of immediate or long-term ill-effects. It should meet the State and Local water quality standards. Many a time, the supplied water is contaminated with pathogens and other dissolved solids, which are harmful. In many countries, people suffer from acute or chronic illness due to drinking of contaminated water. The United States is known to have one of the purest water supplies in the world. The effect of water pollution differs based upon the source and the concentration.

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 drinking water. About 1 billion people don’t have an access to safe drinking water. Mostly water is present in the oceans (97%) and glaciers (2%). Since ocean water is saline, it cannot be used directly.

Water source can broadly divided into two - surface water and ground water. Rainwater contributes to both surface water and ground water. 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. Ground water contains lots of dissolved minerals. The outcome is that all water is not potable, but polluted in one way or the other. Thus, water needs to be treated to meet certain standards before using it for consumption. There are various types of water pollution such as groundwater pollution, surface water pollution and so on.

Let’s take a look at the present scenario of drinking water. According to the World Health Organization (WHO) report, 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 uses improved drinking water through piped household water connection made available inside the user’s dwelling, plot or yard.
• Around 33% population uses 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 uses unimproved drinking water sources such as unprotected dug well, unprotected spring and surface water (river, dam, lake, pond, stream, canal, irrigation channels).

Drinking Water Purification Methods

Drinking water purification is the process of removing undesirable biological and chemical contaminants from raw water, so as to make water fit for human consumption. Water purification systems are different from wastewater treatment plants. Sometimes, purification is also done so as to meet the standard of chemical, medical and industrial applications. There are public and private organizations, which deal with water safety and provide useful information relevant to drinking water issue.

Let's look at various methods of purifying drinking water. It is to be noted that if the water is colored or muddy, it should be filtered through clean cloth or allowed to settle down before undergoing any of the purification procedure.

Bottled Water: Bottled water is treated and safe water that is packaged for human consumption. It is ready-to-use water and hence very convenient as compared to raw water, which needs further purification. But the main drawback is its cost, not everybody can afford buying bottled water.

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

Filtration: Water filtration is one of the water purification process in which the contaminants are physically removed using a filter. It has a benefit of giving immediate access to drinking water without adding an unpleasant taste. The size of the contaminants getting filtered depends on the pore size of the drinking water filters, thus the filtrate can be the smaller bacteria (0.3 µm) or the large parasitic cysts (5- 30 µm). Drinking water filters differ from normal water filters. The major disadvantage of filtration is that it can’t filter viruses. Also, it is expensive and even a micro-crack in the medium allows passage of unfiltered water. So, 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 a better option than the normal filters.

Chemical Treatments: Chemical treatment is one of the most important drinking water purification methods. In chemical treatment, purification is achieved by using chemical halogens. The most commonly used chemicals for drinking water purification are chlorine and iodine. The effectiveness of this method depends on the temperature of water and its turbidity, the chemical concentration and the contact time.

Chlorine in the form of bleach is used for disinfecting drinking water. The amount to be added depends on the concentration, for example, for 5% concentration, add 2 drops per liter and vice versa. The major drawback is the chlorine flavor. Also, study has found out that chlorine is not effective against Giardia. Iodine is more reliable than chlorine in disinfecting drinking water. Iodine is available in the form of crystals, tablets and in solution form. Iodine kills almost all the disease-causing microorganisms. The major drawback of using iodine is its taste. It is advised not to use iodine for pregnant women and for those who are allergic to iodine.

It is to be noted that both chlorine and iodine are not effective against cyclospora, a diarrhea-causing bacteria. Also, there are certain flavor kits available for retaining the water taste. The kits should be added only after the contact time; otherwise it will precipitate the halogen.

Ultraviolet Purification: Ultraviolet water purification is one of the most effective and fast water purification methods. The ultraviolet radiation inactivates the microbes by destroying their DNA (Deoxyribonucleic Acid), thus preventing the microbes from reproducing. It has certain advantages as compared to chemical water treatment. Ultraviolet radiation is effective against all sorts of microorganisms and also it restores the water composition and flavor.

Prevention of Water Contamination: It is always advisable to prevent water pollution as far as possible. The most common cause of water pollution is sewage runoffs, also called as municipal waste. The household waste should be disposed to proper waste disposal sites far away from the water sources such as rivers and lakes. By taking care in everyday life we can help protect the environment as well conserve water.