What is the outcome if water vapor is not adequately removed from the air in the system?

The outcome of not adequately removing water vapor from the air in the system can lead to the potential formation of ice. This is particularly critical in aviation, where ice can form on sensitive components such as air ducts and in the environmental control system. As the aircraft ascends and temperatures drop, excess moisture can freeze, obstructing airflow and potentially causing malfunctions in the air conditioning and pressurization systems.

In contrast, the other options don't accurately describe the implications of insufficient water vapor removal. Increased cabin pressure is related to the pressurization systems and not directly to moisture levels. Improved air quality would typically result from effective moisture control, rather than a consequence of neglecting it. Similarly, enhanced oxygen levels are not a result of moisture presence but depend on the cabin's air management and the proper functioning of the oxygen systems, which are separate from humidity issues.