Things I've learned from Water Aerobics...

Your core abdominal muscles do not engage without conscious thought.
You should roll your shoulders back to lower them and press the shoulder blades closer together (it's ok to stick your chest out) It's better posture and causes less neck and shoulder stress.
When you walk, you should do both of these things...if you are like me, that's hard work.
Balance has to be practiced to be maintained as you get older.