Min. Number of Fixtures

What kind of project do you have? For NC projects, you should include all applicable fixtures that your occupants/visitors will use. Are there no toilets? Otherwise, there is no required minimum, as long as you've accounted for all fixtures in the project.

To meet the requirements of the Indoor Water Use prerequisite, you can base it on only those fixtures that are within your LEED project boundary. If you want to pursue points under this credit, though, you must include fixtures that your occupants use, even if it's outside of the boundary of your project. From the Reference Guide, main page for this credit: 
"Include fixtures and fittings necessary to meet the needs of the occupants. Some of these fittings and
fixtures may be outside the project boundary." That said, in a typical project, you would need to include toilets and hand washing sinks from the restrooms your occupants would use. Additional fixtures would likely be a kitchen or break area sink, and showers, if your building has these available for use. I have had several projects where we could easily meet the prerequisite with the fixtures that were within our space/scope, but were unable to pursue any points under the credit since the existing fixtures used by our occupants outside of our scope area were older and provided no savings over the baseline set by LEED.