Assuming you are going with a single ended bulb, If you mount the lamp using a typical reflector/base setup that should put the lamp roughly 3-4" below the reflector and hood, the reflector can be attached directly to the canopy without worries.

Anything in particular you'd expect that would be splashing water 8" from the water surface to give you concern? That's generally considered a safe distance from the water to avoid splashes, and provides enough working room to avoid the telltale burn marks on your hands/arms.