This tool continuously generates fluid from the surface of an object, and is similar to Source from Volume. Both create a continuous flow of fluid; however, this tool is can be applied to both open and closed volume objects. Source from Volume cannot be applied to open objects, such as grids or curves because they do not have volumes.
Keep in mind, this tool generates volume based fluid, as opposed to the Emit Particle Fluid tool which generates particle based fluid.
If you are sourcing from an object that deforms, or collides with a deforming object, the solvers (smoke solver, fluid solver, and pyro solver) do not pay attention to the per-point deformation. You need to set the Velocity Type to Point Velocity, which is a parameter on the Fields ▸ Sources subtab of the solvers.
Using Source from Surface
Create an open geometry object within a container.
Select the geometry object to generate the source.
Click the Source from Surface tool on the Volume Fluids tab.
Select the container to put the source into and press Enter to confirm your selection.
This tool is different than using Smoke from Object, Burn from Object, and Liquid from Object because it emits fluid continuously. It also useful as it allows you to create and simulate multiple objects in the container, whereas the other tools set the initial conditions from one object.
If the object is only partially in the container, only the portion of the object that is in the container’s boundaries will be simulated.