What is the difference in functions between internal waterstop and external waterstop?

External waterstops are applied externally on the structures and they proved to be effective when installed on the face with a net clamping pressure. For instance, external waterstops can be placed on the outer face of a basement to guard against water entry into the basement.

Internal waterstops are applied internally within the thickness of concrete and it is usually adopted when water pressure can act in both ways. They proved to be effective measures to guard against water flow in both directions but its success lies on the proper installation of waterstops inside the concrete structure. For instance, the installation of waterstops inside concrete slab encounters the problem of improper compaction of concrete around the waterstops.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.