[Delphinus]

I know my floor creaks, snaps, and groans for some time after someone's had a bath. The house is new and I'm not worried about it but it goes to show that the forces involved are having an effect.

Like I said earlier though my guess is that it's OK. But for the love of goodness don't listen to ME because I tend to learn everything the hard way through the school of hard knocks. I always heard the addage that 75 gallons was a pretty good threshold for a tank on an upper floor. Not sure what it was based on. But the premiss was that 75g and under was never an issue, anything above 75g should have a little forethought put into it (ie., not necessarily "don't do it" but at the same time, do consider the variables). Having said that, I've never heard of a tank causing a floor to catastrophically fail and contents of said floor relocated to the basement in a free fall sort of way. More likely though water spilling can drip through and cause different sorts of problems (mold in carpet underlay or in walls, or hardwood swelling, etc.).