Do you think more water runs when 5 people are in 2 bathrooms, or when 5 people are in 1 bathroom?
The enclosed area and the materials that make up the bathroom are also resources. And after 20 years, the sanitary fixtures end up in the trash. And yes, when you share the bathroom, it is more likely that you consider time and water consumption because you don't always have everything available.
I am very surprised by the answers that are at the thinking level of a child. It is not that hard to understand that not only water is a resource. Thinking resources, on the other hand, can be used as much as possible. That harms no one.