If you are using a bump map instead of a normal map you need probably to increase in Tools > Options > Advanced the settings BumpStrengthFactor and BumpDistance. Try 10 and 100 respectively. Each time you change these values either rerender or toggle away and back to Raytraced mode.
You may also refer to the links mentioned in Sea / ocean material, bump and displacement not showing - #2 by nathanletwory . The first link in that post shares a material designed to be used on the ground plane for wavy water.