1. adj. 
Pertaining to the adhesion of a liquid to the surface of a solid. In water-wet conditions, a thin film of water coats the surface of the formation matrix, a condition that is desirable for efficient oil transport. Treatments that change the wettability of the formation from water-wet to oil-wet can significantly impair productivity.
2. adj. 
Describing the preference of a solid to be in contact with a water phase rather than an oil or gas phase. Water-wet rocks preferentially imbibe water. Generally, sandstones and carbonates are water-wet before contact with crude oil, but may be altered by components of the crude oil to become oil-wet. Certain minerals, as well as different crystallographic faces of the same mineral, may be variably prone to being oil- or water-wet.