21 CFR §890.5100

1. (a)Identification. An immersion hydrobath is a device intended for medical purposes that consists of water agitators and that may include a tub to be filled with water. The water temperature may be measured by a gauge. It is used in hydrotherapy to relieve pain and itching and as an aid in the healing process of inflamed and traumatized tissue, and it serves as a setting for removal of contaminated tissue.
2. (b)Classification. Class II (special controls). The device, when it is a hydromassage bath or a powered sitz bath, is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 890.9.