In a bathroom the humidity levels are usually far above the average -%. On one hand the rooms are small, on the other hand a lot of moisture is released there. Almost every time the bathroom is used, water will flow. Whether one is washing their hands, using the toilet, taking a shower or bath; in some small homes the laundry rack is often put up inside the bathtub to dry wet clothes. Without a sufficient amount of ventilation, mould is bound to grow.

A protection against liquid ingress is imperative for rooms with higher-than-average humidity (bathroom, laundry room, kitchen) as well as outdoors to withstand weather. Some devices can handle humid air but not water jets, meaning they are suitable for damp indoor rooms but not for outdoors. On the other hand, some units can even be completely submerged in water for a short period without suffering any damage.