At the atomic level it is very different that’s why service tension is a thing.
Water forms hydrogen bonds with other water molecules but it won’t form hydrogen bonds with oxygen (under normal temperatures) molecules. So under the surface water is bonded to other water on all sides. But on the surface it’s only bonded to water below it under the sides, above it is unbonded. When water makes something wet it doesn’t bond to that thing so they’re still separate elements, but the surface of the water is making a barrier between itself and the bonded water. Resulting in different properties.
I can’t think of a compelling reason to treat the water on the surface as a distinct entity, though.
At the atomic level it is very different that’s why service tension is a thing.
Water forms hydrogen bonds with other water molecules but it won’t form hydrogen bonds with oxygen (under normal temperatures) molecules. So under the surface water is bonded to other water on all sides. But on the surface it’s only bonded to water below it under the sides, above it is unbonded. When water makes something wet it doesn’t bond to that thing so they’re still separate elements, but the surface of the water is making a barrier between itself and the bonded water. Resulting in different properties.
It seems to me that being bonded, at all, to other molecules, is a better criteria for being “the same thing”.