Tenant doesn't install water fixtures - can automatically get 1 point for Option 1 - water analysis?

No. You generally do not get a point awarded for doing nothing.

Marcus is correct. Some additional insight:

• For the IP worksheet, I have similarly asked about fixtures when not in scope. I recall LEED Coach telling us that the IP credit asks the team to document considerations in early design, and it shouldn't necessarily reflect the actual design. In this context, you can still populate the water sections of the IP worksheet with conversation topics that the team could/should have had aroud decisions to include/exclude fixtures, and meet the documentation expectations of the reviewers.
• For the WE Prereq, if there are truly no fixtures added as part of the tenant scope, then the Prereq is N/A; in these cases, the project is not eligible to pursue/attain any points under the associated Credit.
• There may be a scenario where there are fixtures in the tenant scope, so the project documents compliance with the Prereq via these fixtures only; the associated Credit might not be pursued if the base building's fixtures are not water-saving, for example (like in many existing building contexts). In this case, pursuit or exclusion of the Credit was by choice.
• For projects where the tenant has their own fixtures and wants to pursue points under the Credit, all fixtures used by the project's occupants must be included in the Credit (but not the Prereq) calculations, whether they are in the tenant's LEED boundary or elsewhere in the building.

I have seen a project or two add 1-2 low-flow fixtures (like a cafe sink) within their own space to enable them to meet the Prereq as well as pursue points in addition with the base building's fixtures (when the fixtures were favorable). This could be seen as gaming the LEED system by some (depending on project circumstances), but the project is playing the points game rules that LEED set up.