Water based paints means the medium used for manufacturing and thinning is water and solvent base paints, the medium is solvents like MTO, Xylene, etc.

Interior emulsions are designed to perform in interior atmosphere and will not be suitable for exterior surfaces. If it is applied in exterior, fast deterioration will happen and the decoration will be lost in very small duration. 

Primer is an undercoat for paint. It provides excellent adhesion and provides excellent durability for top coat.