Water Pasteurization and the WAPI

One way to make water safe to drink is to pasteurize it.  Pasteurization is accomplished by heating the water to 65°C (149°F) for a short period of time.  The water is then free from microbes, including E. coli, Rotaviruses, Giardia and the Hepatitis A virus.  Pasteurization is not sterilization, so although this water is safe to drink, don’t use it for medical procedures.  Pasteurization also does not remove sediment from your water, which could be greatly reduced by pre-filtering the water through a cloth prior to pasteurization or allowing it to settle and skimming the clear water off the top.

Although you’ve probably heard you need to boil your water to make it safe to drink, the water actually only has to reach 65°C (149°F) which is NOT boiling temperature to be safe to drink.  Boiling is used as a visual indicator that the water has reached a temperature high enough to be pasteurized.

Water can be  heated to pasteurize it on a stove or by using solar power.  To use the sun, a solar oven is ideal, but other methods can get your water hot enough to pasteurize it as well.  Try the dash of your vehicle, a metal roof, or just a black container in the sun on a hot day.  But if the water doesn’t reach boiling point, how will you know it has gotten hot enough to eliminate the disease causing microbes?  Here’s where the WAPI comes in.

WAPI (pronounced WAH-pee) is an acronym for Water Pasteurization Indicator.  It is a simple, inexpensive temperature indicator consisting of a clear plastic tube about 1 3/4″ long with a heat sensitive soy wax inside.  The tube is connected to a wire or fishing line with weights at the ends or suspended from a float so the wax is on the top of the tube suspended in the unheated water.  The wax melts at 150°F (65°C) and will all fall to the bottom of the tube after 6 minutes at that temperature, indicating the water has been pasteurized and is safe to drink.  Because the melted wax will stay at the bottom, you’ll know your water reached pasteurization temperatures even if it has cooled before you check it.  After the wax cools, the tube can then be inverted and used again and again.

I have one of the simple style WAPI’s strung on nylon fishing line.  The trouble with this design is that if you are using a heat source other than solar, the line can melt where it touches or hangs over the pot.

In my research I found that the two major retailers for them have both redesigned their WAPI’s to overcome this problem.  Sun Ovens International has designed theirs to snap into the bottom of the container it comes in, allowing it to float in the water, and Solar Cookers International has strung theirs on a stainless steel wire.  I personally really like the fact that mine is strung on a string which allows me to insert it into a narrow neck container like a water bottle.  The float system would be difficult if not impossible to use in a narrow neck container, but would work great if you’re heating water in a pot.

Where can I get a WAPI?

Solar Cookers International–stainless steel wire style, $9.00 shipped.

Sun Ovens–floating style, $9.00 shipped.

Both are better models than the original with fishing line, so take your pick.  And for that price, go ahead and get a couple extra so you can heat more than one pot at a time.

Keep preparing!
Angela