OK now that we have the information you can use this:
that you place on the water. Read it through to know what to do (exemple, enable Send Collision Message)
Add a collider box to your fire, tag your particle system with Fire_tag (or else) and you should be good to go.
P.S: I do not have Unity to try it so I might have missed a detail...
answered Jul 14 '12 at 04:32 PM
Colliders will do it. I dont know how the fire and the water will be featured in your game, but basically you could add a collider to the fire prefab and check if it is hit by water. If you use colliders or cast a ray, sphere or whatever against it depends on how youre going to implement it of course. Then, if hit, simply destroy the fire object and the fire is out.