Do they overlap?
What is the 'comparative advantage' of each concept over another?
What? IWRM is essentially about governance?
Ah, you mean the human right to water is essentially about governance?

What is 'not' governance?
What 'is' governance?

What? Did you just asked, if these concepts actually works?
Well my friend, theories always work in theory, but seldom in practice.
What really matter is not whether it works or not, but whether its coherent :)