Water aerobics is wonderful cardiovascular exercise. If that's something you enjoy doing, keep doing it.
As far as walking, it's not a surprize that you feel winded as well as pain when you're on land. When you're in the water, the water helps support your weight. It also helps to cushion your joints. You don't have that cushion when you walk on land.
One thing I'm going to recommend is that if you make sure you're wearing a good pair of walking shoes. Get fitted at a reputable walking/running store. wearing the right shoe while walking will help reduce some of that pain you're feeling.
Another thing is if you can only walk for ten minutes. That's all you do for now. there are members who could barely walk to one end of their block and back. that's where they started. This week you do ten minutes. Next week, maybe you try for 11 or 12 minutes.
If you continue to walk, with time and regular practice, your strength and endurance will increase. start with that ten minutes. As you lose weight, that will also take stress off your joints, making it easier to walk.
So, don't be afraid to take short walks. Stop when you need to stop. You will get stronger. Keep up your water aerobics. Not only is it a great workout, but it's a terrific way to reduce stress too.