Do you need group fitness certification in order to teach Aqua Fit/Aqua Aerobics?

Technically, you do not need either unless required by the employer or local government. There are other possible regulations that may impact this as well. Insurance may be required in some areas and to get liability insurance as an instructor, most companies require some type of certification. A facility may be able to cover the classes without the instructor being certified. Hopefully, this is one area that will be better regulated soon. A minimum level of proven education is definitely needed.