can the landlord require me not to use the bathroom for shower?

[theartfullodger]

Did the inventory mention the shower in question??

[Dan_Manchester]

I agree with Westminster, if the T installed a shower without consent and the use of that shower caused damage then the T is liable for 100% of the damage (back to the state at the start of the AST minus fair wear and tear).

You knew that there was only one shower when you moved in, not the LL's fault that you then changed your mind and want two.