# Boil 3, Add 1 Method

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The **Boil 3, Add 1 Method** is a proposed method to reduce fuel use when pasteurizing water without the need of a thermometer.

* Please note:* This method needs to be validated by testing in the field.

## The problem

Everybody knows that water contaminated by pathogens can be made safe to drink through boiling. Solar Cookers International co-founder Dr. Bob Metcalf, a microbiologist, confirmed in an article in APPLIED AND ENVIRONMENTAL MICROBIOLOGY (Feb. 1984) [1] that water could be made safe to drink using much lower pasteurization temperatures (65°C or 150°F), thus saving fuel.

Even though the fuel savings of pasteurization make it preferable to boiling, boiling is still commonly recommended because the rising bubbles are a clear indication that boiling temperatures have been reached. In order to achieve the fuel savings of the lower pasteurization temperatures however, a thermometer is needed, since there is no known simple way to know that 65°C has been reached.

To use the Boil 3, Add 1 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 (33°F) (the coldest temperature where water is still liquid) to 3 measures of boiling water resulted in 4 measures of water at 78°C (173°F), which is well above the temperature where water is made safe to drink instantly. Mathematics predicts that the resultant temperature should have been 75°C (167°F), but the residual heat in the pot may have contributed to the higher experimental temperature.

## Steps for use

- Select a container appreciably smaller than your cooking pot.
- Pour 3 containers full of water into the cooking pot.
- Heat the water to boiling.
- As soon as the water starts to boil, add 1 container full of cold water to the boiling water.
- 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 (181°F), as it is at an altitude of 5000 meters. 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 a few degrees(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 (155°F). At 5000 meters a ratio of 2:1 would result in water at 67.5°C (153.5°F).

## External links

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