The biggest models are same size as biggest IBM Power machines, i.e. 2 four-post racks connected together.
You then need liquid cooling connection, power (iirc the racks can contain internal UPS). You're still left with need for storage which can go from a shelf to maaaany racks, related networking gear (ethernet and FiberChannel) and that's it, but a lot of it would be common to any serious enterprise DC.
As far as I can tell, they don’t need external water connections. While everything serious is liquid cooled, they have on-rack radiators. The z17 machines are shipped with the cooling circuit sealed, so it doesn’t need to be filled before use. Power consumption is also relatively low because that’s one demand their clients have that they don’t expand much on top of z16. They are very power-efficient machines.
My only complaint is that there’s no desktop or desk side version. Using z/OS as a daily driver would be an interesting challenge.
I am not up to date on latest ones, but it used to be that depending on chosen density you could have "air" cooled meaning sealed liquid cooling with on-rack radiators, and denser units with heat exchanger for external cooling loop.
You then need liquid cooling connection, power (iirc the racks can contain internal UPS). You're still left with need for storage which can go from a shelf to maaaany racks, related networking gear (ethernet and FiberChannel) and that's it, but a lot of it would be common to any serious enterprise DC.