Water is undoubtedly the essential and basis for life to exist on the planet earth. Water exists abundantly in all three states i.e. solid, liquid and gaseous states on the earth. We human beings are closely associated with water in everyday life. On the average, humans consume 2.5 litres of water each day, although it varies depending on age, gender, climate etc. The percentage of water in human body also varies according to age and gender. The average adult male has about 60 % water and adult woman has about 55% water, because women naturally have more fatty tissue than men and fatty tissue contains less water than lean tissue. The percentage of water in infants is much higher, typically around 75-80 %, dropping to 65 % by one year of age. People feel thirsty when they lose around 2-3 % of their body water. As water in the body is lost, mental performance and physical coordination start to become impaired and no human being can live without water for more than 3-5 days. Now a days, people has got more awareness on the health benefits of drinking pure water. People who are above poverty line are preferring to drink purified water than normal tap water. In this article, I discuss about the water we drink in different forms in our daily routine life to quench our thirst.
Normal water or tap water or ground water is common form of water that many people consume every day. Pure water is odourless, tasteless and colour less whereas ground water has taste and varies from region to region. The taste we feel in the ground water is due to dissolved chemicals and minerals like Calcium, Magnesium, Zinc, Iron, Sodium, Potassium, Chlorides, Nitrates, Fluorides and Bicarbonates. Apart from these, many harmful microbes exist in ground water and hence it is considered unsafe to drink tap water without purification. Many water born deceases spread out due to drinking of contaminated water and hence all health experts suggest to purify normal tap water before drinking.
Boiled water is what doctor advise us to take during ill health condition. Water boiled and cooled enough to drink and it is the one of the oldest technique of purification. When water is boiled enough, all the microbes in water die at high temperature and is free from germs. Hence, taking boiled water is considered healthy. Further, it is the easiest way of purification, affordable and can be done readily at home. However, boiled water still contains unwanted dissolved chemicals and minerals which cannot be removed by just boiling. Hence, boiled water is although a quick method to purify water, it is not at all a complete purification.
Distilled water is more purified water than boiled water. In the process of distillation, water is boiled to steam and all the germs will be killed. The steam is then condensed again by cooling. The condensed water thus obtained is pure .But, in this process, a variety of organic compounds and certain impurities such as Silica, ammonia etc. will still remain. But this process is not viable and easy to carryout in our home. Rain water is close to distilled water as the heavy down pour is due to similar cycle of evaporation of surface water and then condensation of clouds formed. But, direct drinking of rain water is not advisable.
Carbonated water or Soda water is one of the most commonly available product in the market. Carbonated water is prepared by mixing Carbon dioxide gas in water. At room temperatures, Carbon dioxide does not dissolve in water. It is dissolved in water by mixing the gas at high pressure and low temperature. When temperature increased or pressure is reduced by opening the bottle, CO2 gas in released forming bubbles. Club Soda, flavoured cool drinks etc. are all carbonated waters with added flavours and sugars. Carbonated water is a diluent. It dilutes alcohol, spirits and is widely used as an alternative soft drink. Carbonated water has slightly sour taste with PH between 3 and 4. An alkaline salt such as sodium bicarbonate is commonly added to soda water to reduce the acidity and to improve taste. Studies shown that carbonated water erodes tooth enamel but the effect is negligible. On the other hand, it is common experience that the carbonated water eases the symptom of indigestion and constipation troubles.
Activated Carbon Filtration
The method of carbon filtration is widely used in home water purifiers. Carbon is extremely porous material and can absorb thousands of different chemicals. Activated carbon is a carbon which has slight electric positive charge added to it making it more attractive to chemicals and impurities. Generally, activated carbon filters used in home water purifiers typically contain either granular activated carbon or powdered block carbon. Activated carbon filters are usually rated by the size of the particles they are able to remove, measured in microns and generally ranging from 50 microns (least effective) to 0.5 microns (most effective). The two most important factors affecting the efficiency of activated carbon filtration are the amount of activated carbon in the unit and amount of time the contaminate spreads in contact with it. Granular activated carbon remove many volatile organic chemicals, pesticides and herbicides as well as chlorine, benzene, solvents and hundreds of other man-made chemicals found in tap water. Activated carbon filters cannot remove sediments and visible particles, so they are often preceded by a pre sediment filters which is used to eliminate gross contaminants that would otherwise clog the activated carbon there by reducing the surface granules available for absorption. Further, activated carbon filters cannot remove dissolved inorganic contaminants or minerals and salts (hardness, scale causing contaminants) like Antimony, Arsenic, Cadmium, Beryllium, Nitrates, Asbestos, Chromium, Sulphates etc. and certain radio nuclides. Removing these contaminants require more efficient method of purification which is achieved by reverse osmosis (R-O) filtration system in our houses. Before discussing RO filtration, we shall see some of the disinfection techniques that are adoption for purification of water, because, RO filtration is done in combination with any one of the water disinfection method.
The water is purified by adding powerful oxidants to disinfect it from microbes and bacteria to prevent the spread of water borne diseases. Although these process are not used in our houses, they are done commonly in public water distribution of drinking water.
Chlorine is a powerful disinfectant and is added in public water supplies to kill pathogens. Dissolved in water, chlorine converts to an equilibrium mixture of chlorine, Hypochlorous acid (HOCl), and Hydrochloric acid (HCl). This solution alters the concentration of chemicals in and around bacterial cellular fluid and drastically inhibits the multiplication of bacteria, there by eventually dies. Chlorinated water has slightly pungent smell and in some circumstances, it reacts with naturally occurring organic compounds found in water and produce disinfection bi-products some of which are found to be harmful for health. Now a days, disinfection Chloramine is also becoming common as there are less serious bi-products with Chloramine than Chlorine.
This process involves mixing of ozone through electric discharges in water. Ozone oxides the iron, manganese, and sulphur in the water to form insoluble metal oxides or elemental sulphur. These insoluble particles are then removed by post-filtration. Ozone rapidly reacts with bacteria, viruses and has strong germicidal properties than chlorine. Disadvantages of ozonisation is that it involves special techniques to dissolve in water, high operational cost, and cannot persist in water as after affect residual in purified water.
In this process ultra violet radiation is exposed to water. UV radiation is produced from fluorescent lamps by ionising low pressure mercury vapour. Ultraviolet light radiation is powerful enough to break bonds of cellular genetic fluid of microbes, there by microbes eventually die or prevent multiplication process. However, UV radiation is used as supplement to other sterilization techniques.
Reverse Osmosis Filtration (R-O filtration)
Osmosis is the spontaneous net movement of solvent molecules through a partially permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. The process of osmosis can be opposed by applying pressure in the region of high solute concentration with respect to low solute concentration. Reverse osmosis is a widely popular separation process that uses pressure to force solvent through a semi permeable membrane that retains the solution the solute on one side and allows the pure solvent to pass through the other side. In reverse osmosis purification technology, water is allowed to pass through under pressure through very thin membrane coils, which has pore size of 0.0001 microns, and as a result pure water is obtained which is devoid of dissolved minerals. There are basically two membrane types: CTA (cellulose triacetate) and TFC (thin film composite). CTA is chlorine resistant. TFC is more efficient than CTA; however, TFC membranes are sensitive to chlorine, so if you have chlorinated source water, you must buy a system with a carbon pre-filter to remove the chlorine.
The process is best explained in the animated video here under.
Generally, RO filtration units purifies water in various stages:
- A sediment filter to trap visible particles.
- An activated carbon filter to remove volatile chemicals.
- Reverse osmosis filters to remove dissolved minerals and organic chemicals.
- Ultraviolet lamp to sterilize microbes if any leftover even after RO filtration.
The above stages are repeated depending on the design of purification system. The RO system filtration combined with active carbon filtration and other techniques is most effective and widely used now a days for house hold purposes with compatible RO filtration units available in the market for affordable prices. This method is also widely used to purify large quantity of water especially for desalination etc. in water purification industries. One of the disadvantage of RO filtration is that it removes some of the dissolved minerals in water which are good for our health. Further, the process requires enormous amount of water. These systems typically return 5-15 percent of the water pushed through the system and a good outlet is to be provided for draining out waste water.
Mineral water bottles are commonly available in the market and are often considered as purified water. Mineral water is generally prepared in large quantities for commercial purpose by processing water in various stages like sediment filtration, sand filtration, micro filtration, carbonation, ozonization, activated carbon filtration, RO filtration, UV filtration etc. The various stages involved in purification process of mineral water makes it slightly acidic and also removes minerals which are good for health. So to compensate, some of the minerals which are good for health are added in right proportions after purification to neutralize the water, hence the name mineral water.
Apart from purification of water, the storing of water after purification is also very important in our houses. Many people store and drink purified water in plastic bottles or other containers which are not thoroughly cleaned. The purpose of purification is often lost in un-hygienic storing of water. As science and technology is advanced, the purification methods of drinking water are also improving and drinking water is now a days, a man-made product ! Drinking pure water is the first positive step in maintaining good health.