Not sure I agree. The other comments seem to say that office buildings are designed for a certain amount of water capacity. So even if you supplement (?) and add nodes (?) there's still a bottleneck of capacity. So, if water collected in tanks on each floor then it can be dripped out (so to speak) to not exceed capacity.
Even if total wastewater disposable capacity was the issue (which would be surprising considering the highly correlated toilet use in many office buildings after breakfast and lunch), the more fundamental problem is that the drain pipes are not distributed in a way conducive to residential use, or put another way, most people don't want communal bathrooms.
Drains need to be sloped to the riser pipe. And in nearly all offices thats concentrated in the middle, which implies a huge slope for drains coming from several dozen feet away.
