Nice Tattie 
 Was this created with planes on top? 
The next set of material editing for skyline will allow the detail layers to be used which means you could have a rain puddle texture and blend it with the ground, we hope anyways lol 

 Then use scaling and offsets to get the correct amount of puddling and then use the opacity of each layer to blend it in 

Would be cool to have rain over surfaces. 

Thanks for sharing.