There is provided an air treatment apparatus including an air flow generator that is arranged to generate an airflow, a moisture source that is arranged to introduce water vapour into the air flow, a body that in use surrounds both the air flow generator and the moisture source, a water supply system that is arranged to provide water to the moisture source, the water supply system including a water tank assembly that is separable from the body, an interface sealing element that is arranged to form a seal between the water tank assembly and the body that prevents leakage of air into the body, an air supply feed that is arranged to convey air from within the body of the air treatment apparatus into the water tank assembly, and one or more air filter assemblies that are located upstream of both the moisture source and the air supply feed.