Abstract: A device for holding the corner of a sheet and/or cover in place on the surface of a water bed mattress is provided by a corner structure insertable under each corner of the mattress, to be supported and confined by the bottom support for the mattress and the upright side walls of the mattress confining frame. Each corner structure includes a diagonal brace member with mitered ends adapted to abut a pair of transverse side walls of the mattress confining frame, and to define a generally triangular space between the brace member and the adjacent frame corner. A mattress lifter, that is part of the device and is smaller than said triangular space, is hingedly mounted to the brace member and positioned in the triangular space. A handle means is secured to the mattress lifter and provides manual means for pivoting the mattress lifter about its hinge so as to raise the corner of the water bed mattress that is positioned thereabove.