Why Is Chlorine Added to Drinking Water and Swimming Pool Water?

Chlorine is one of the most abundant of the 92 naturally occurring elements found on our planet. It is highly reactive, so it readily combines with other elements to make a variety of different compounds. Scientists have learned to utilize chlorine's abundance and high reactivity to their advantage and have formulated numerous chlorine-containing chemicals with thousands of purposes. One such purpose is to kill disease-causing organisms (pathogens).

History

• Chlorine was discovered by Carl William Scheele in 1774, long before scientists understood the cause and spread of disease. It was not until 1854, that Dr. John Snow demonstrated that the disease cholera was transmitted by water. Even though the association between disease and water had been made, the cause of illness remained a mystery until the 1870s, when Louis Pasteur and Robert Koch developed and expanded upon the germ theory of disease. In 1881, Robert Koch demonstrated that chlorine kills bacteria.

Disease and Water

• Waterborne diseases are those in which water serves as the mode of disease transmission. Such diseases include, but are not limited to, cholera, typhoid, and dysentery. The addition of very small amounts of chlorine to contaminated water quickly kills bacteria and other microorganisms. The chlorine begins its path of destruction by first attacking the pathogen's cell wall and membrane. It then deactivates cellular enzymes and structures needed for the pathogen's reproduction and survival.

Drinking Water

• Drinking water becomes contaminated with microorganisms when it comes in contact with human or animal feces. Only slight contact is required to cause disease. Flood waters, septic systems, landfill water runoff, and sewer pipes are possible sources of drinking water contamination. Since 1905, when the use of chlorine for drinking water disinfection began, the number of deaths from waterborne disease has greatly decreased. Unfortunately, unsafe drinking water remains a threat to human health, particularly to children in underdeveloped countries.

Swimming Pool Water

• In addition to contaminated drinking water, untreated swimming pool water can also cause disease. Again, human and animal feces are the most common cause of contamination. Fecal residue from the bodies of swimmers is a common source. Direct contamination of the pool water with the feces of birds and rodents is also likely. In addition to feces, human body substances such as saliva, mucus, and shed skin cells may cause infection. Proper chlorination of swimming pool water kills pathogens and prevents the spread of disease.

Advantages and Disadvantages

• The advantages of chlorine for use as a water disinfecting agent are numerous. Chlorine is readily obtainable, inexpensive, and has the capacity to kill most microorganisms. It is convenient to use because it dissolves easily in water, and is available as a solid, liquid, or gas. Chlorine also leaves a residual that continues to kill pathogens after the treated water has left the treatment plant. This residual is responsible for the disadvantageous taste and odor that accompanies chlorine-treated water. The fact that chlorine is toxic and must be handled carefully is another disadvantage.