Wet Wall Surface

Hi all, I was wondering if you could help me figure out how to make a wet surface shader, after water has touched the surface. For example, when a room is flooded and the water is drained, I would like the affected areas to still be wet, and then slowly dry, going downwards. The best example I can show you is the image attached to this post.

I can’t seem to find any other tutorial or post that explains this effect. So any help in the right direction to get me started would be greatly appreciated.