A pop-up water jet assembly comprises a housing having a vertical, central axis, an upper end, a top surface, a lower end, an interior and a water inlet adjacent to the lower end communicating with the interior of the housing. A pop-up member having an upper portion, a top surface, a lower portion and an interior in communication with the interior of the housing, is movable relative to the housing between a raised position in which the upper portion of the pop-up member extends from the upper end of the housing and a lowered position in which the top surfaces of the housing and the pop-up member are substantially flush. The upper portion of the pop-up member carries a water outlet nozzle communicating with the interior of the pop-up member and having an axis at an angle to the axis of the housing to discharge water directed in a trajectory away from the pop-up jet assembly, the pop-up member being movable to its raised position in response to water flow admitted into the housing through the inlet and to its lower position under gravity bias upon termination of the water flow. The water discharged from the outlet nozzle may be illuminated by an optical fiber or LED light source mounted within the housing. Also disclosed is a water reservoir system such as a spa incorporating a pop-up water jet assembly in accordance with the invention.