Wikipedia says to bring water to 85 C for several minutes to kill pathogens
http://en.wikipedia.org/wiki/Portable_water_purification
they refer to the same studies often referred to here
So, I figure 90 C for 2 minutes would be good. If it was a little less probably okay.
If I do 90 C instead of boiling (100 C) I'll save about 10% on fuel. If I also turn it down so it takes almost twice as long, and use my heat exchanger windscreen I save about 25% – 0.2 oz of fuel to heat 1 pint of water.
That will enable me to use a small canister (4 oz) for one 5 day trip. Or 8 oz canister for two trips.
So, how hot is 90 C?
I measured on my patio. Thermometer through hole in lid slightly above bottom:
When the temperature goes above 80 C, lots of tiny bubbles form on the bottom of the pot, and they break, so it starts making a hissing noise. A little hard to hear if I'm next to a stream or it's windy or I'm using my Pocket Rocket.
90 C takes another 30 seconds. There are many tiny bubbles on bottom and it's noisier. Some foam on top.
If I'm at 9500 feet elevation then 90 C is boiling so you have to get to full boil.
I'm never that high but 5000 or 6000 feet is pretty common, so half way in between.
When I reach 90 C, I just turn off stove with lid on pot and let it sit for 2 (or 5) minutes.
About half my water is for tea, which I like to steep for 5 minutes, so I just put tea bag in when it starts getting hot. Swish it around. Put on lid. Let it reach temperature. Turn off. Let it sit for 5 minutes.
For oatmeal or soup, when it gets to temperature, I turn stove way down to prevent scorching, put in food, stir, put back on lid, let the stove go for another 10 or 20 seconds, turn off and let sit 5 minutes for food to re-hydrate.
