I decided that my rain needed some fog to be more realistic and ambient, so added a height based fog component to my scene.
I changed the colour to match the teal of the water and the night sky and added some more fog for increased ambience.
I liked the way this looked, however there was a transparency sorting issue where the water was not being affected by the fog. Answerhub suggested that this might be to do with the plane’s tesselation, so I smoothed out one of the planes. This didn’t do anything though.
In the end, I deleted the atmospheric fog, as the two don’t work well together and this elivated some of the issues. Its still not fantastic, but it looks ok.