Yes, IRRIGATE is a Scrabble word!

Letter values in Scrabble US: I 1, R 1, R 1, I 1, G 2, A 1, T 1, E 1.

Is it a valid word?

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

supply with water, as with channels or ditches or streams
supply with a constant flow or sprinkling of some liquid, for the purpose of cooling, cleansing, or disinfecting