Yes, BACKWATER is a Scrabble word!

Letter values in Scrabble US: B 3, A 1, C 3, K 5, W 4, A 1, T 1, E 1, R 1.

Is it a valid word?

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

a body of water that was created by a flood or tide or by being held or forced back by a dam
a place or condition in which no development or progress is occurring