[quickthrowman]

> You'd also have to install a bunch of showers, which could be a significant problem on its own.

Compared to installing a new domestic water pipe riser and drains in an office tower (plus pumps, pressure tanks, etc), installing a shower in each unit is essentially free.

Connect the in-unit supply lines to the tap, core drill a hole in the floor to get to the floor below and connect to the drain piping, done.

[mothballed]

You can also just raise the shower and toilet on a platform, plumb the waste directly to the wall while depending on the platform to buy you some vertical slope on the way out, and drill right through the side of the building and run the waste vertically down the side. It's not going to freeze on the way down unless you're in Yakutsk. The supply lines you might not even have to retrofit, just put a pressure tank on each floor for peak loads that are slowly topped off by the undersized supply lines.