Indoor Water Use Reduction - Core and Shell : Binding tenant agreement only for a part of the building

Hi Michaël, I can comment on what I've experienced, and we'll see if anyone else chimes in. If your C/S client truly has no qualifying fixtures in the base building scope, they would be exempt from the Prereq, and would not be eligible for any points under the Credit. If they want to pursue savings using all/only tenant-installed fixtures, then yes, I have been told that they must have the signed agreements in place for all tenant spaces. For any scenario that claims savings from tenant fixtures, they would need an agreement signed by both parties. An owner commitment, alone, is no longer accepted in v4 going forward. I have not attempted nor asked about a combined approach (kind of surprised it hasn't come up, actually) where your calcs would be partially C/S scope and partially tenant-installed with a signed agreement. In this scenario, I would assume the approach would be that the C/S fixtures must still meet the Prereq alone, and any savings could be claimed by separate, supplemental calcs combined with the C/S calcs for the Credit. This would theoretically apply where the building is not yet fully leased at the time of submission.
While this approach sounds logical and fair, since it deviates from both allowed scenarios as written in the Reference Guide, you would definitely need to reach out to LEED Coach / GBCI for clarification before assuming it would be an accepted approach.  If you do ask about it, please report back. This is an interesting question. Anyone else?

I agree with Emily's response. One item to add....If the local code requires flush/flow rates lower than the LEED baseline you can claim associated savings of code-compliant future fixtures. 

Oooh, good one. I have looked for this before on my C/S projects, but my locations haven't worked out yet for it.