Can you use water base exterior paint inside also?

It's best not to assume it is safe to do this. First ask a professional painter or a specialist paint store for advice. Even though they are water based some paints contain very toxic chemicals (drying agents, etc.) whilst being applied and after they have dried. They are not dangerous to human or animal health if used properly in the open air but are simply not safe to use indoors. Always read the notes on the tin!