The problem of adhesion between a cylinder and a plate with a water bridge in between is solved exactly. The adhesive force needed to separate the cylinder and plate at constant volume of water or at constant humidity is shown to be different and both are unstable except for a small distance at constant volume. For large contact angles and constant volume of water the curvature of the water/air interface can change sign during separation. Increasing the contact angles between water and cylinder or between water and plate reduces the adhesive force. The adhesive force decreases with increasing humidity. The experiment, which used silicone oil instead of water, to keep volume constant, agrees with the calculations.