I don't know for certain, but I doubt it's illegal. HOWEVER, my concern would be that the water drips somewhere, someone else steps in it, and you have war on your hands!
After posting this I will see if I can find anything official.
On edit, approved cleaners (for use during play) are those that don't effect the hardness of the ball, or have abrasives. Any approved cleaner must be completely wiped/dried off before delivery of the shot. With that in mind, it shouldn't alter the lane condition more than any other approved cleaner being used by someone else.
Water seems to qualify here, if dried off, UNLESS, it drips on the floor, and causes someone to stick or otherwise deface the approach (rule 12).