This is according to Google:
adjective
1.
covered or saturated with water or another liquid.
So, water can be wet, as water can be covered with water. However, a single molecule of water won't fit this definition.
Covers implies some kind of boundary between a material of some type and a material of another type, something that can be independently observed and not just asserted.. it kind of loses all meaning if you drop this. If you put water on water you don't have water covering water, you just have water.
