In our Mastrick bathroom in Aberdeen, a countertop basin sits on custom units beneath the window. Pale walls and floor help give the dedicated shower and basin a consistent setting. The window position brings a design choice that is easy to miss when looking at furniture in isolation. The place where you wash your hands need not determine the only place you can comfortably use a reflection.
When considering a basin at the window, draw the places where you will wash and get ready before selecting a mirror location. Try a view facing the window and another facing a nearby wall. Consider where daylight falls on the face at each position and whether both places can be used while the room is occupied. The useful arrangement may keep washing and grooming close while giving each a sightline that works.
