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Chlorine: a vital water disinfectant - March 2006
Chlorine-based disinfection has a long history: the first time bleach was used to disinfect water was in 1897 to combat a typhoid outbreak in Maidstone, Kent (UK). Water chlorination has played a role in extending life expectancy from 45 years in the early 1900s to 76 years today (World Health Organization). The use of chlorine and filtration to purify drinking water was cited by Life Magazine (1997) as “probably the most significant public health advance of the millennium.” Chlorination is by far the most common method used globally to disinfect wastewater. It kills pathogens, and prevents their accumulation in fish, shellfish and other aquatic organisms. It also destroys a variety of bacteria, viruses and protozoa, including Salmonella, Shigella and Vibrio cholerae. Another area where chlorine-based products offer benefits as disinfectants is in swimming pools, helping ensure safe access to this popular sport for many people. One such disinfectant is calcium hypochlorite – Ca(OCl)2, a white solid – which is added to pools in granular or tablet form. Used properly by well-trained pool operators, this destroys germs that are capable of causing numerous health problems for pool users: diarrhoea, swimmer's ear (a severe earache) and various respiratory, skin and other infections. Spa and hot tub water can also be disinfected with calcium hypochlorite, which has the advantages that it can be easily transported and stored for a long time. World Water Day is celebrated each year on 22 March by a different United Nations agency. This year UNESCO's theme is Water & Culture - how people perceive and manage water in the world's different regions. Visit the World Water Day website for more information. Key role in developing worldCalcium hypochlorite is also used to disinfect water in many small water systems serving communities in the developing world. One example of such a community is the village of Yamaranguila, home to 2,500 people living in the mountainous southwestern part of Honduras. Yamaranguila has a simple water supply system using spring water which flows naturally from underground. This water is disinfected with calcium hypochlorite and stored in a large tank. Pipes deliver safe drinking water, by gravity, to homes. (The gravity system takes advantage of the mountainous terrain.) Historically, this system worked well. However, by 1998, it was simply not able to supply enough water for the growing community. Recently, the system was upgraded - thanks to a grant from the Water Relief Network, a global programme of the chlorine and PVC industries. A new, larger water storage tank was constructed and old pipes were replaced with durable, relatively inexpensive PVC water pipes. Before Yamaranguila began chlorinating its drinking water in 1987, it was tragically common for children to die of diseases caused by drinking unsafe water. Today, in Yamaranguila, as in Western Europe, it is rare for a child to die of a water-related disease. Responding to a global crisisMore than 1,000 million people in the developing world are not as lucky as the residents of Yamaranguila: they do not have safe drinking water. Even within the World Health Organization’s European Region – which includes more than 50 countries - over 41 million (5%) do not have access to a safe drinking water supply. Worldwide, diarrhoeal illnesses cause 1.8 million deaths every year, according to the WHO. Most of those who die are children under five years old. A point-of-use disinfection system consists of very simple equipment. People who collect their drinking water daily from lakes, rivers or wells are able to disinfect their water before using it. A bottle of liquid or a packet of solid treatment chemicals is provided along with a water storage container. The chemicals, which may include calcium or sodium hypochlorite, are measured into the water container. Point-of-use treatment is certainly not as convenient as centralised water treatment, but evidence shows this simple, low-cost method reduces the risk of diarrhoeal disease and death. Even in the developed world, point-of-use systems can be life savers when natural disasters, such as earthquakes and hurricanes, disrupt water supplies. Clean, safe water is a public health necessity, and calcium hypochlorite helps to provide it where it is needed most. Text based on the original produced by the Chlorine Chemistry Council (US). |
Chlorine acts as a powerful disinfectant when used either on its own, as sodium hypochlorite (bleach) or as calcium hypochlorite. Added to water in minute quantities, it quickly kills bacteria and other microbes. Chlorine has the major advantage of ensuring clean water right up to the tap, whereas the action of other disinfectants - such as ozone, ultraviolet light and ultrafiltration - is only temporary. In addition to purifying water, chlorine helps remove tastes and odours, controls the growth of slime and algae in mains pipes and storage tanks, and helps to remove unwanted nitrogen compounds from water. Over 90% Europe's drinking water is chlorinated, and Europeans drink around 400 million glasses of tap water every day.