You might think that untreated water must be at a rolling boil, which occurs at 212°F (100°C), for at least one minute in order to be safe to drink. Without any kind of temperature gauge, this is good advice to follow for water purification.
What many people don’t know, however, is that water does not need to reach 212°F to kill off all the nasty stuff. It only needs to be pasteurized, which occurs at a significantly lower 149°F (56°C).
Simply put, the WaPI, or Water Pasteurization Indicator, is a basic, easy to use, and reusable thermometer that allows the user to know for sure when water has reached a high enough temperature to be safe to drink. Pasteurization kills all microorganisms that lead to disease from drinking contaminated water.
Temperatures Required to Kill Microorganisms/ Water Purification
Protozoa Cysts – Giardia, Cryptosporidium, Entamoeba
Bacteria – V. cholerae, E. coli, Shigella, Salmonella typhi
A WaPI device is a small plastic tube containing soy wax that melts at 149°F. It will save precious fuel (wood, charcoal, gas) by eliminating the need to heat water all the way to boiling. Even better, it is possible to achieve pasteurization only using the heat of the sun and a solar oven, making this process ideal for camping and in emergencies.
How to Use Your WaPI
1. Pour water into a black pot, a jar, or bowl.
2. Set the WaPI into the container with the wax at the top of the cylinder. The WaPi should be in the deepest part of the center of the container. It should not touch the sides or bottom of the container. If you have to use extra fishing line in order to get the WaPI properly placed, do so.
3. Put the pot in the solar oven.
4. When the wax melts and slides to the bottom of the WaPI, the temperature has reached 149°F and the water is safe to drink. Plan on this taking about one hour per liter of water in full sun.
5. The water needs to cool before drinking and should stay covered to prevent recontamination. Keep your fingers and any other objects out of the water. If you think it’s been recontaminated, simply re-pasteurize the water.
6. Once the wax in the WaPI has solidified again, turn it upside down and use it for the next batch of water!
It is important to note that dangerous chemicals are NOT removed by pasteurization. Do not attempt to drink water you think may be contaminated with chemicals, even after pasteurizing.
Pasteurization is NOT the same at sterilization. Heat resistant spores that survive pasteurization are harmless in drinking water, but can be deadly in other uses. This process should NOT be used to prepare water for medical needs or for certain food canning processes.
You can use your WaPI in water being heated over an open flame source if you choose. Newer WaPIs are made to withstand high heat.
WaPIs are often included with the purchase of a solar oven, or you can buy them individually. Consider purchasing one for each vehicle and one for each bug out bag. They also make a nice, inexpensive gift for a survival minded friend.
More resources for water purification
- Big Berkey Water Filtration System — dependable brand, recommended
- Katadyn Gravity Water Filter — 1 to 6 persons
- Lifestraw Personal Water Filter — inexpensive and lightweight
- The Prepper’s Water Survival Guide by Daisy Luther
- Sawyer Complete Water Filtration Kit — one of the best brands
- Sawyer Mini Water Filter — a good size for emergency kits. I keep one in my suitcase for family travel.
- Survival Mom: How to Prepare Your Family for Everyday Disasters and Worst Case Scenarios by Lisa Bedford
- Survival Still – a water distillation kit
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