A flush-mounted group for mixing water for a bathroom or kitchen, comprising: a body comprising a valve, designed to be installed in a seat having a given depth with respect a finished surface, a fastening means for fixing the body to the seat, which is adjustable on the body to set the depth at which the body is inset inside the seat, a plate mountable on the finished surface to enclose the body inside the seat and which is provided with an opening for accessing the body, a control member for operating the valve, which is connected to the valve through the opening of the plate. The mixing group comprises a coupling means for connecting together the valve and the control member, which can be adjusted so as to vary a distance between the control member and the valve and ensure correct positioning of the control member inside the opening.