# Analog of fluid mass in electrostatics

I have just finished watching Khan Academy tutorial on divergence. Therein he uses fluid velocity to represent vector fields. Positive divergence at a point represents source of mass at that point.

Comparing it with the expression $\vec \nabla. \vec{E}$, it is evident that electric field is the analog to fluid velocity.

However it seems to me that we cannot make charge as the analog of fluid mass. This is because over the whole vector field domain, we have fluid mass present. But we don't have electric field present over the whole electric field domain.

So in electrostatics, what shall we make the analog of fluid mass?

• There would usually be electric field present over the whole space. Instead, there would likely be no electric charge at most points. Perhaps there is a typo? – edm Mar 17 '18 at 8:37