Ah - the 10% water addition hypothesis! In my youth (many, many years ago) I did a series of tests to ascertain what impact this actually had in my trangia. My results were somewhat predictable; had a small effect on sooting, increased burn times (ie getting water to boil) by about 10-15% (nearer 15%) and shortened overall length of burn by about the same amount. In short, the burner was about 15% less efficient.
My theory for these results - and I am totally open to correction on this! - is as follows
- at Trangia temps, water doesn't split down into hydrogen and oxygen atoms - it simply turns to water vapour/steam. So it doesn't add any additional combustible fuel to the mix.
- Some of the heat produced by the alcohol burning is used to convert the water into water vapour (you don't tend to get a remnant of water in the trangia burner when the burn is finished, indicating that any water present has been vapourised.)
- The water vapour itself may act to wash away a bit of the soot present on the bottom of the pan, leading to the slight improvement on the level of sooting found.