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A simple way to pasteurize more water with less fuel without the need for a thermometer...

Please note: The following article is posted as a proposed method of determining water pasteurization temperatures without the use of a thermometer. Note that this method needs to be validated by testing in the field!

The Boil 3, Add 1 method is a proposed way to make more water safe to drink while using less fuel in a way that does not require a thermometer. To be safe to drink water doesn't have to be boiled (see Water pasteurization); it only has to reach 65°C (150°F) and maintain that temperature for 20 minutes. At 71°C only 15 seconds are required to completely deactivate all disease-causing organisims.

If one has a thermometer, it is very easy to heat water to these temperatures and know that it is safe to drink. The Boil 3, Add 1 Method provides a way to add boiling water and cold water together in such a way that no thermometer is necessary.

Using this method, one brings 3 measures of water to a boil and then adds 1 measure of cold water. A quick practical test at sea level showed that adding 1 measure of water at 1°C (the coldest temperature where water is still liquid) to 3 measures of boiling water (100°C) resulted in 4 measures of water at 78°C. Mathematics predicts that the resultant temperature should have been 75.25°C, but the residual heat in the pot may have contributed to the higher experimental temperature.

Steps for use

  1. Select a container appreciably smaller than your cooking pot.
  2. Pour 3 containers full of water into the cooking pot.
  3. Heat the water to boiling.
  4. As soon as the water starts to boil, add 1 container full of cold water to the boiling water.
  5. If your altitude is below 2000 meters your water will be safe to drink immediately. Above 2000 meters, wait 15 minutes before drinking the water.

Sea level variation: Boil 5, Add 2

The normal "Boil 3, Add 1" method works at any any altitude up to 2000 meters since it takes into account the fact that water boils at a lower temperature at higher altitudes. At sea level, however, one can mix the water in a proportion of 5:2 instead of 3:1 and arrive at a temperature of 71.7°C. This variation allows for more water to be pasteurized at sea level with the simple rule of "Boil 5, Add 2."

Topics for research

The above method was designed to work even if the colder water is close to freezing and the boiling temperature is only 82.8°C at an altitude of 5000 meters. This design for the worst-case scenario is necessary for this method to work 100% of the time and to be easily communicated with others. However, humans are able to determine when water is lukewarm (body temperature) within some range (as yet to be tested). This lukewarm water could be added in a proportion of 1:1 with boiling water and pasteurization might still be achieved (mathematics shows that the resulting temperature at sea level would be 68.5°C. At 5000 meters a ratio of 2:1 would result in water at 67.5°C.

External links

  • Excel spreadsheet for calculating the resulting temperature when mixing quantities of water a different temperatures

See also