Abstract: A hot and cold water mixer comprising: a mixer body defining a hot water inlet conduit and a cold water inlet conduit opening towards a mixing chamber communicating with a water delivery orifice; the mixing chamber has therein a mixing unit operably driven, by a control handle or knob, between a closed position, a hot water or cold water open position, and a mixing position. The mixing unit comprises a stationary disc of ceramic material having first and second apertures communicating with said hot and cold water inlet conduits, and a movable block of ceramic material having a flat face sealingly sliding against a flat face of said disc; said block has a cavity opening to said flat face and respectively to the side surface to define a water passage from said inlet conduits to the mixing chamber, the width of the block cavity being larger than the distance or spacing between the apertures in said ceramic disc in order to communicate with either or partially with both the apertures in said disc.