Are you talking about an existing fountain or new construction? If existing, try to keep the conduit out of the water, usually the fountain water is treated with chemicals to inhibit growth etc. No telling what this may do to your raceway. If new construction, no reason you couldnt run PVC in the slab, I dont think a fountain would be under section 68, even if it is accessible to the public. Best to check with your AHJ to be sure.