that may depend on the facility where you teach. When I used to teach water aerobics, I needed neither one of them. But at another facility, I was required to be certified in community water safety which means that I had to demonstrate the skills of helping somebody get out of the water in the event of an emergency.
They often don’t, but I would recommend it. I teach aquatic exercise to participants from football players and elite athletes to seniors and people living with Parkinson’s. I have my lifeguarding cert because I want to know that I am ready to act in an emergency. I have known some elite swimmers who had a sudden illness or even a cramp that nearly cost them their lives in the water. Well prepared instructors and coaches are what made the difference between a drowning and minor incident.