at least here in my area (Raleigh, NC), it would be a matter of finding a club that partners up with the Arthritis Foundation to offer aquatic classes. It usually requires a pool that has a higher than normal temperature (about 89 + degrees F), and those facilities are not that easy to find. You would need to become an instructor at that facility. I would check out YMCAs first as they tend to work with the Arthritis Foundation.
I teach water aerobics, and some instructors teach what we call “Range of Motion” classes which are geared towards people with arthritis. At least at my facility, it is required that you hold an aquatic group exercise certification. I looked at your profile and was not sure whether your certification was for water of land.