Solar pasteurization is the use of heat or radiation to kill microorganisms. Water only needs to be heated to 1490 F for approximately 6 minutes to kill parasites, bacteria, and viruses.11 In fact, 99.9% of water pathogens will be destroyed.
If you have a solar cooker, a dark covered pan filled with contaminated water can be set on the solar cooker. The solar cooker is sealed to trap the air which is heated by the sun.
The heated air then heats the water. However, during a disaster a purchased solar cooker may not be available. In that case, you can build a solar pasteurization system using simple materials.
- Dig a pit approximately 4 inches deep and 3 feet wide
- Line with natural materials like leaves or grass about 2 inches deep for insulation, making a lower area in one corner (trough)
- Cover the insulation with a layer of clear plastic and a layer of black plastic so that the plastic edges run up the sides of the pit and extend outside of the pit
- Add water approximately 3 inches deep
- Place one end of a hosepipe or tubing in the trough for siphoning the pasteurized water, clipping the other end closed
- Place a WAPI in the trough
- Cover the pit with clear plastic
- Cover the clear plastic with wadded paper creating an air space
- Cover the wadded paper with clear plastic and make sure the sheet edges are weighted down with dirt or rocks
- When WAPI indicates water is pasteurized, siphon off the water
The question is: How do you know when the germs have been killed? A Water Pasteurization Indicator (WAPI) is the answer. It is a simple device for determining when water has reached the right temperature for pasteurization. A purchased WAPI contains a special soy wax that melts at pasteurization temperature. You can build your own WAPI with very simple supplies.
To make your own:
- 1. Place a bead of glue on the inside of a straw approximately one-half inch from the opening
- 2. Pinch the straw close
- 3. Make a tiny hole in the closed straw end with a needle
- 4. Melt beeswax into an eyedropper
- 5. Drip the melted wax into the open straw end until the wax is about one-fourth inch tall
- 6. Place a bead of glue on the inside of a straw approximately one-half inch from the opening on the other end of the straw
- 7. Pinch this end of the straw close (now both ends are pinched flat)
- 8. String fishing line through the small hole made on one end of the straw and tie it into a loop
Beeswax will melt at pasteurization temperature. The homemade WAPI is placed in the water and when the wax melts, the water is safe to drink. However, the homemade WAPI should only be used when you are unable to buy one.