How to Test if Water Is Pasteurized

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Short Description

  • Problem: Testing if water has been pasteurized properly
  • Idea: Using a tube with a wax that melts at 69 degrees, above the pasteurization temperature
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The World Health Organisation (WHO) estimates that 80% of all diseases are caused by infected/contaminated water. Therefore pasteurisation (destroying disease carrying organisms like bacteria, parasites and viruses) of drinking water is very important. This is also a worry for trekkers and tourists as they travel to very remote places with little or no medical facilities. To kill disease carrying organisms you do not have to boil water. Water is pasteurised at 65oC (149oF). Some heat resistant spores can survive the pasteurisation, but they are rendered harmless. An easy way to test if water is pasteurised is by using a Water Pasteurisation Indicator

The WATER PASTEURISATION INDICATOR (WAPI) is a sealed tube with a special white wax (soy bean fat or brazilian carnauba wax) inside. The wax melts at 69oC (156oF) just above the temperature needed to pasteurise water, that is when your water is safe to use. The thermometer is a transparent plastic tube that has been crimped and fused at both ends using heat. Inside the tube is a small amount of wax which melts at 69 degres celsius. The rest of the is filled with air. The thermometer is placed in the water pot with the wax at the top. A metal ring slides along the tube to hold the opposite end of the tube at the bottom of the vessel. The air in the tube then acts as a float to position the wax away from the bottom. This is necessary since water at the bottom of a solar cooker may be very hot due to its contact the black heat absorbing tray. When the water has reached 69 degrees, the wax melts and falls in the bottom of the tube. This indicates that the water reached the pasteurization temperature.

Photo shows a water pasteurization indicator ready to place in a pot of water (left) and after registering water pasteurization temperature (right.)


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Dr. Robert Metcalf 1324 43rd St. Sacramento, California 95819 USA.

Dale Andreatta can be contacted at dandreatta(at)

Derek Yegian at dtyegian(at)


  • Purchase a WAPI at :[[1]]


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