May 2004
For many of us, the word "chlorine" brings to mind thoughts of summertime and the cool, refreshing water of swimming pools. The chlorine we think of in connection with summer fun is usually the chemical compound calcium hypochlorite, Ca(OCl)2. Calcium hypochlorite is a white solid that is added in granular or tablet form to pool water to kill germs that can make swimmers sick. Used properly, by well-trained pool operators, this compound destroys germs that are capable of causing numerous health problems for pool users--diarrhea, swimmer's ear (a nasty earache) and various respiratory, skin and wound infections. Spa and hot tub waters are also disinfected with calcium hypochlorite--it's a chemical wonder that makes healthful water recreation possible. But there is much more to the story of this chlorine compound.
One of the Family of Chlorine Disinfectants
Chlorine water disinfectants are public health champions, prolonging and improving life wherever they are used. Large water systems--those supplying tens or hundreds of millions of gallons of water per day--in the US and Canada use mostly chlorine gas (Cl2) or
sodium hypochlorite (NaOCl) to disinfect drinking water. Smaller water systems--those supplying less than about five million gallons per day--often use calcium hypochlorite. Calcium hypochlorite is easily transported and stored for long periods of time.
Calcium hypochlorite is also one of the allies in the ongoing fight against foodborne disease. It is mixed with water to various strengths to kill germs found on industrial food processing and preparation surfaces--an important role in keeping our food supply safe. Other chlorinated disinfectants include chlorinated isocyanurates.
Helping to Bring Clean Water to the Developing World
Water pipes being installed in Yamaranguila, Honduras
Calcium hypochlorite is 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 that uses spring water that flows naturally from underground. This water is disinfected with calcium hypochlorite and stored in a large tank. Pipes deliver sanitary drinking water, by gravity, to homes. (The gravity system takes advantage of the mountainous terrain.) This system has worked well, however in 1998, the village water system was simply not supplying enough water for the growing community. Recently, the system was upgraded--thanks to a grant from the Water Relief Network, a global program of the chlorine and
polyvinyl chloride (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, unfortunately, common for children to die of diseases caused by drinking unsanitary water. Today, in Yamaranguila, as in the US and Canada, it is rare for a child to die of a water-related disease.
Responding to a World Crisis
More than a billion people in the developing world are not as lucky as the residents of Yamaranguila-they have no access to safe drinking water. As a result, diarrheal illnesses cause 1.8 million deaths every year, according to the World Health Organization. Most of those who die are children younger than five years old.
The member countries of the United Nations (UN) have set a goal to cut in half the percentage of people in the world without access to safe drinking water by 2015. This is a great challenge considering that poverty in much of the developing world prevents building even simple water systems such as the one in Yamaranguila. To make chlorinated water more available to many of these poor people, point-of-use systems are being distributed.
A Very Special Home Use
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 to disinfect. Point-of-use treatment is certainly not as convenient as centralized water treatment, but evidence shows this simple, low-cost method reduces the risk of diarrheal disease and death.
Even in the developed world, point-of-use systems can be a life-saver when natural disasters, such as earthquakes and hurricanes, disrupt water supplies. Clean, safe water is a public health MUST and calcium hypochlorite helps to provide it, especially where it is needed most.
What is a Part Per Million?
The Association of Pool & Spa Professionals recommends keeping chlorine levels between 1.0 and 4.0 parts per million to maintain good water quality in pools. What is a part per million? It is a unit of very low concentration. Think of it as one in a million--1 in 1,000,000.
The following comparisons can help us put "one part per million" in perspective:
One inch in 16 miles
One minute in two years
One cent in $10,000
Follow-Up Questions
- How would your life be different if you did not have access to clean drinking water? Write an essay explaining how your daily activities would be affected.
- Write the fractions that represent one part per thousand, one part per million, one part per billion and one part per trillion.
- Draw a diagram that shows where your drinking water comes from and how it is treated before it flows from your tap.
For a list of previous "Chlorine Compound of the Month" features, click
here.