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Sterilizing Water
Name: Ryan A.
Status: Student
Age: 17
Location: N/A
Country: N/A
Date: March 2004
Question:
I am doing a project on water sanitization and boiling the water (as everybody knows)
kills all bacteria. Well, research shows that bacteria does grow back if not properly sealed right
so how can I keep bacteria down to the lowest possible level?
Replies:
Boiling water kills MOST bacteria. Do not forget about those that live in the volcanic vents at the
bottom of the sea. As a practical matter, however, you need to exclude both air (oxygen actually)
and organic matter. Life forms as we know them require those two ingredients (We will withhold judgment
until the data from Mars is in.). As an aside, deionized water found in many chemical labs is not
biologically pure. There are strains of harmful bacteria that survive in the DI water lines, so DI
water should not be used to make coffee or tea.
Vince Calder
You have made an incorrect assumption. Boiling does NOT kill all bacteria. There are bacteria that
form spores, which are structures that help them to survive harmful environmental conditions, such as
drying and high heat, etc. Spores can withstand boiling. To truly sterilize something, it must be
free of all microbes AND spores. In most cases this must be done in an autoclave or pressure cooker.
At atmospheric pressure, the boiling point of water cannot go higher than 212 deg. F. So to get the
temperature to go higher, we must raise the pressure. This is what an autoclave does. Autoclaves
are expensive, but a pressure cooker can be purchased at Target or Walmart, etc. One must be careful
to follow the directions very carefully though as the contents are under pressure and will be hotter
than boiling. As long as the liquid is covered so nothing can get in, after autoclaving or pressure
cooking it should be free of microbes until it is opened again.
vanhoeck
Well Ryan, as a matter of fact, boiling does not kill ALL the bacteria, just MOST of them. Some
bacteria are actually resistant to the temperature of boiling water (100 degrees C.). To kill all
the bacteria, you need to raise the temperature to about 121 degrees C. To get water to this
temperature, you must heat it under pressure. (You cannot heat boiling water in an open pot to
anything
over 100 degrees C.). In science labs, we use something called an autoclave to do this; at home
you might have a pressure cooker in the kitchen. Pressure cookers are used for sterilizing things
like canned foods, so that harmful bacteria will not grow in them.
Back to your question. Start with a bottle of water. Loosen the cap a bit so it will not burst.
Cover the cap and neck of the bottle with aluminum foil to prevent bacteria from being deposited
near the lid at some later date. Heat for 20 minutes at 121 degrees C. in a pressure cooker or
autoclave. Let cool and tighten cap. That water, my friend, will stay sterile indefinitely.
Paul Mahoney
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Update: June 2012
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