I think that's my event horizon. In any case, the technique I eventually found to get it working in-camera was really, really stupid. I wonder if it still works post-Lightwave 2018? Something to check.
Anyway, my solution was;
Gradient color texture, light blue in the center and dark at the edges.
Fractal noise reflection map (I think I used a little one that came with Lightwave's stock content package, but anything should work)
Rippling animated bump texture.
And, the trick: Ramping the reflectivity of the puddle up to insane levels, 1000%, 10000%, I don't remember, at the center, and "just" 100% at the edges.