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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 pasteurize a given amount of water using less fuel, without the need for a thermometer. To be safe to drink water doesn't have to be boiled (see Water pasteurization); it only has to be heated to 65°C (150°F). If one has a thermometer, then it is very easy to heat water to this lower temperature and know that it is safe to drink. The Boil 3, Add 1 Method provides a way add hot and cold water together to be able to pasteurize water when no thermometer is available.

Using this method, one brings 3 measures of water to a boil and then adds 1 measure of cold water. A quick practical test shows 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) will result in 4 measures of water at 78°C (which leaves a margin of error of 13°C since a safe pasteurization temperature is 65°C).

Steps for use

  1. Select a small container much smaller than your cooking pot.
  2. Pour 3 containers full of water into the cooking pot.
  3. Heat the water to boiling.
  4. Add 1 container full of cold water to the boiling water.
  5. The water is now safe to drink.

Things that you should note

  • Add the cold water as soon as the water in the pot boils so that the hotter water isn't reduced in volume by evaporation.
  • Water boils at a lower temperature at higher altitudes. At sea level one can mix the water 5:2 instead of 3:1, which gives you more water for a given amount of fuel.

Topics for study

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 ration 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