I’ve only worked at a few places that have pools, but it seems to be more variable with aqua fitness than land-based fitness. Check with the place that you’d like to work. Some places require both. One place where I used to work requires neither, but you had to mentor directly with the pool manager.
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.