You probably already know a few ways to do this, but none that beats this method! It will not only make you be able to start a combustion with a drop of water, but it will be the coolest GREEN flame!
For a brief description please watch this video:Note: Alot of people have mistakenly claimed that I have stolen video and pictures for this Instructable. To clear everything up, I didn't steal anything, I simply posted elsewhere long time ago, and eventually it became popular on the internet. Look in the beginning of the video for the signature.