They had a white gas fountain at the Burn a couple of years back, they just injected white gas into the top tier of a fountain and lit it up.

Some friends of mine did a propane version with sand that worked really nicely, haven't seen water, though, you'd have to make sure you have Very small bubbles, or it may prove hard to keep lit...

i have done this twice now, its a really cool and very simple effect.
first project was to bubble propane out of a small jet under water in small pond in friends back yard, it worked really well but i had to tweak the gas pressure just right to get it to stay lit. It look like the pit of eternal stench bog from labyrinth!
next time i did this was with a bronze fountain i made, i simply tee'd the output from the pump with a orificed propane feed and got a bubbly propane out put with the water. The effect was really pleasing, again, i had it o tweak the pressure just right to maintain a burn on top of the water. But damn, what a cool effect, the propane falls burning down the side of the fountain and looks like liquid fuel!
I have not done that since, but i support you efforts, and by the way, eventually the water gets hot, so use a bronze impeller pump.
J..

Thanks for all the great input guys. The fountain in the pictures is really cool. But not quite what I have in mind. Justin seems to be on exactly the same page as me. Did your water get boiling hot? And did you observe much smoke from the thing?

Ideally I'll be able to use this as a heat source in a semi-sealed up tent. I want to end up with a small firepit like contraption that three or four people can sit around and stay warm.

I think I'm going to look into a portable natural gas tank as well, probably cost prohibitive, but I like to know my options before I get carried away.

I've got the entire xmas week off from work, if I can tear myself away from the forge, I'm going to play with this idea and get the scale of it figured out.