What are lavatory facilities on an aircraft primarily used for?

Lavatory facilities on an aircraft are specifically designed to provide restroom services for passengers and crew members. These facilities ensure that there is an appropriate and hygienic space for personal sanitation needs during the flight. They are equipped with essential features such as toilets, sinks, and sometimes additional amenities to maintain cleanliness.

The other options do not accurately describe the primary purpose of lavatory facilities. Preparing meals is typically done in the galley area of the aircraft, while storage for emergency equipment is often located in designated areas that are separate from the lavatories. Likewise, resting areas for crew members are usually located in crew compartments, which are also distinct from lavatory facilities. Thus, the primary function of lavatories is to provide necessary restroom services.