What type of systems need to be functioning in the lavatory?

The correct choice focuses on the essential systems required for the proper operation of a lavatory within an emergency equipment context. In this setting, both the toilet and water systems are crucial because they ensure hygiene and sanitation for individuals onboard. The toilet system must be functional to provide a means for waste disposal, while the water system is necessary for handwashing and maintaining cleanliness.

In situations where emergency preparedness is vital, the lavatory must be equipped to manage basic human needs, thereby directly impacting the overall health and safety of the users. A failure in either the toilet or water system could render the lavatory unusable, leading to potential hygiene issues and decreased morale among users.

While lighting systems and emergency alarms can be important for safety and visibility, they do not directly contribute to the basic operational function of the lavatory in the same way that the toilet and water systems do. Hence, focusing on the functionality of the toilet and water systems underscores the critical aspects of lavatory operations in emergency situations.