It sounds like you are trying to create a fake, non-transparent water material.  If so, then plug your specularity map into the "Variable Specular Channel" on the Highlights tab (just click the "Variable Highlights" checkbox).  However, a better way to create a sheen across water is to use a standard Vue water material (which is transparent) and then play with the Flare Intensity and Size parameters on the Transparency Tab.  Flare is equivalent to highlights for transparent materials.