Yes, LIMPIDITY is a Scrabble word!

Letter values in Scrabble US: L 1, I 1, M 3, P 3, I 1, D 2, I 1, T 1, Y 4.

Is it a valid word?

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

free from obscurity and easy to understand; the comprehensibility of clear expression
passing light without diffusion or distortion

Not playable in Scrabble US: PELLUCIDITY, PELLUCIDNESS.