Polarization imaging [1] could probably do it. Granted, the sensors are expensive and lower resolution than one might like.
Another way is to measure surface specularity. Use one or more IR spotlights at different angles to the surface and strobe them on and off. A wet surface will have a different angular variation in reflectivity vs a dry surface, unless the floor is very shiny.
Another way is to measure surface specularity. Use one or more IR spotlights at different angles to the surface and strobe them on and off. A wet surface will have a different angular variation in reflectivity vs a dry surface, unless the floor is very shiny.
1. https://thinklucid.com/tech-briefs/polarization-explained-so...