Being required or not really doesn't matter when it comes to rent. A renter is not paying for the construction of the house. The renter is not having the house constructed nor are they buying the house. That is all the owner. The renter is paying for the use of the house, for a set amount of time The landlord isn't adding a fee because it has a bathroom. In the aspect of goods and services, rental of an item, in this case is a house, is a service, as you are paying for the use of the house for specific time, and do not gain ownership.
Your alarm scenero would be catogarized as business expense.
So.. you went from saying that landords charge a fee for a bathroom and it's baked in.. which is false. So you move to try and argue about the construction costs impling that the renter is paying for the cost of the construction, as if they are having the house built, which is also false.. To now, trying to argue and argue about functionality of a bathroom.. When are you going to stop? See above.
You are confusing "type" of bathroom, Communal or private, with having just having a usable bathroom for a tenant. the price isn't based on having a bathroom in your example, it's based on the type of bathroom in your example. They are also not paying for the construction of that bathroom be it private or communial, they are paying for the use of the residence that so happens to have a communial bathroom.