If you are wondering where in the hell the fluid source node went to in Houdini 17, The genius behind Applied Houdini already has a explainer video for you here.
“Essentially it's a Pyro Source SOP (set to Source Smoke) to create points, an Attribute Noise SOP to mess up the density values a bit, and then a Volume Rasterize Attributes SOP to convert the points into a volume that can be read into the simulation with the new Volume Source DOP node, which needs only to be set to Source Smoke to work properly…”