Pasturization is an extremely useful process in areas where clean drinking water is not readily available.
Filtered water (thru cloth) put into plastic 2 liter soda bottles spray painted black and put in the sun for a few hours (better if put on a refective surface will pasturize the water making it safe to drink.

How to tell the water has reached the required 70 deg celcius temp ? Paraffin will melt at 70 plus degrees. So some container with some solid paraffin (candle wax) inside a silmilar container placed next to the water will be the indicator. When the wax melts, the water is done!
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