Yes, WATERINESS is a Scrabble word!

Letter values in Scrabble US: W 4, A 1, T 1, E 1, R 1, I 1, N 1, E 1, S 1, S 1.

Is it a valid word?

WATERINESS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the wetness of ground that is covered or soaked with water
meagerness or poorness connoted by a superfluity of water (in a literary style as well as in a food)
the property of resembling the viscosity of water