A sillcock for supplying varying amounts of water at various temperatures includes a backpressure relief valve for relieving backpressure in the sillcock. The sillcock includes a sillcock tube and a valve body attached to the sillcock tube. A cartridge assembly is provided in the valve body, and an actuation assembly extends through the sillcock tube. The actuation assembly cooperates with the cartridge assembly to control the volume and temperature of water exiting the sillcock according to the axial and rotational movements of a knob. The backpressure relief valve includes a deformable member operable to allow water to be expelled from the sillcock if backpressure is present.