How to document the water use reduction for CS?

In your case, you must clearly identify which components of this credit will be implemented as part of the developer’s scope of work (toilets and lavatories?), and which portions will be part of the tenants’ scope of work (showers and kitchen sinks). You would need to document your tenant work (showers and kitchen sinks) as ‘neutral’, meaning that you would not calculate any water savings for these fixtures. For example, the showers would have both a baseline and design case water use of 2.5 GPM. If water use calculations include improvements to the tenant fixtures, then the project must provide tenant sales or lease agreements confirming the use of water saving fixtures (e.g. the installation of a shower that uses less than 2.5 GPM).

Along the same lines... working on a C & S where the developer's scope is the toielts and lavatories (used by both tenants), but tenant 1 will install a kitchen sink and tenant 2 will install a laboratory sink. I don't think I have to count a laboratory sink, so that just leaves tenant 1's kitchen sink. My question is would this mean that I would need to create 2 fixture groups and some how divide the FTE between tenant 1 and the rest of building so that I can list tenant 1's sink as only used by tenant one and count it as 'neutral'. Or could I get away with just leaving it out since it's just 'neutral'. I don't see how it would make a difference in the water saving totals.