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< prev - next > Water for Life - Community water security (Printable PDF)
Water for Life 41
Chlorine
Chlorine is cheap and easy to use to kill most germs in drinking water. The difficulty
with chlorine is that if too little is used it will not kill germs or make the water safe. If
too much is used, the water will taste bad and people may not want to drink it.
How much chlorine to add to the water?
The amount of chlorine needed to disinfect water depends on how contaminated
the water is (how many and what kinds of germs it contains). The more germs you
have, the more chlorine you need to get rid of them. It is important to add enough
chlorine so that some is left in the water after the germs are killed. The chlorine that is
left is called free chlorine. This will kill any new germs that get in the water. If the water
has free chlorine in it, it will smell and taste just slightly of chlorine. This tells you it is
safe to drink. If it has too much, the smell and taste will be strong and unpleasant.
To use the right amount of chlorine you need to know how strong your chlorine
solution is. Chlorine comes in different forms — gas, bleaching powder, high-test
hypochlorite (HTH), and household liquid bleach. Because household bleach is
the most common form of chlorine, this book shows how to disinfect water with
household bleach.
Household bleach may have different amounts of chlorine. Most common are 3.5%
and 5%. The easiest way to measure the amount of bleach needed is to first make a
mother solution (about 1% chlorine) and then add this solution to the water you want
to disinfect. First prepare the mother solution:
1. Add 1 cup of bleach to a clean,
empty beer bottle.
2. Fill the bottle with clean water.
3. Shake the bottle for 30 seconds.
4. Let it sit for 30 minutes. Your
mother solution is ready.
If there is a lot of solid matter in the water the chlorine will be less effective in killing
germs. To ensure that chlorine is most effective either filter the water through a cloth
or other type of filter (see page 39) or let the water settle so solid matter sinks to the
bottom. Pour the clear water off into a clean container and then add chlorine.
WAT E R
For 1 liter
or 1 quart
For 1 gallon
or 4 liters
For 5 gallons
or 20 liter
BLEACH
3 drops
12 drops
1 teaspoon
For a
200 liter barrel
10 teaspoons
Add these amounts of the mother solution to clear water and
wait at least 30 minutes before drinking the water. If the water is
cloudy, you need twice as much of the bleach solution.