Yes, HYDRANT is a Scrabble word!

Letter values in Scrabble US: H 4, Y 4, D 2, R 1, A 1, N 1, T 1.

Is it a valid word?

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

a faucet for drawing water from a pipe or cask
a discharge pipe with a valve and spout at which water may be drawn from the mains of waterworks

Also: water faucet, water tap.