I remember animating this scene early on in production of Who Framed Roger Rabbit.
The Disney Archives recently posted these three phases of our process which combined animation with live action.
It was ABSOLUTELY essential that the animation would hide any live action gadgets that were needed to hold real props or create effects, like real water in this case. The animation needed to be on 1s (like the live action), which resulted in a ton of work. But I had a blast working out the technical challenges for each scene. Because I knew that when ILM would send us the final scene (with highlights and shadows) to be shown in London during "rushes" or "dailies" we will see magic.
Video essayist Kristian put this clever and informative youtube film together. It explains how we did some of this stuff: