This reservoir assembly includes a reservoir, a liquid supply module of a downstream pipe, and a level sensor. The bottom has a first protruding portion, for housing the supply module, and a second protruding portion for defining a passage housing the downstream pipe. The level sensor is located in the housing. The bottom further has an upper area and a lower area adjacent to the housing. The upper area is defined by a top portion of the passage. The lower area is located lower than the upper area. The level sensor is in the housing at the same altitude as the lower area.