Water pipes are just like playing with legos! Anything that is a water pipe can be a rig and anything that is a dab rig can be a waterpipe you just have to have the right attachments. A piece with a male joint will need either a female banger or a bowl. A piece with a female joint will need either a male banger or a bowl.
Smaller water pipes are at this time called dab rigs, while larger water filters are called bongs or water pipes.
How a piece is used is more what the user wants to use it for than what the piece is called initially.