The Clue Its on the house?
The Answer TANK
The answer "TANK" fits the clue "It's on the house" because a tank can refer to a large container, often used for storing water or other liquids. In some contexts, a "house" can mean a building that contains a water tank. Additionally, the phrase "on the house" typically means something is free, and a tank can hold resources that might be provided without charge, like water. Overall, the connection between a tank and a house makes this answer clever and fitting.