I'd like to hear other people's opinions on this direction included above:
"Commercial Interiors projects must include in the water-use calculations any water fixtures that are being used by occupants, even if the installation of the fixtures is not within the scope of the project. For example, an office project that is not updating the base buildingwill still need to include the core bathroom fixtures in the LEED water use calculation."

I've heard from numerous sources that core fixtures only count towards this calc with a full floor tenant. For tenants who are only in part of the floor, you only need to include the fixtures within their tenant space (eg their scope of work), not the core.