Less like water ‘spray’ and more like ball-pit!
Does anyone know how to get the foam a more suitable size? It looks fine in the fluid sim (as a point in space), but I can't see a scale value anywhere in the Whitewater Source, Sim or Import nodes.
Thank you.

When rendering particles, the attribute ‘pscale’ can be used to set the point scale per-point. Most of the tools set reasonable defaults, but it looks like whitewater does not. You can use any of your favorite ways for setting and manipulating attributes to create the pscale attribute. Using vex with a wrangle or attrib vop is probably the most efficient way to set the value and vary the size, or if you are using houdini 16, give the new point sop (attribute expression) a shot. If you simply want to set a global scale, there should be a property on the object you are rendering the points from which will act as a global point scale. It's called “Point Scale,” in the geometry tab of the render properties.