You can create an "air pocket" that looks like a real air pocket but can still drown you. 

How to reproduce:

1. Create a body of water that is at least 4 blocks deep
2. Go into survival if you weren't already in that gamemode
3. Type in /give @s bucket 9 
4. Select the buckets and spam right-click until you see an air pocket

The air pocket is not really air, so you can't use it to your advantage.