The correct answer is B) It supplies the operating medium used in the removal of the distillate. The water supply through item "P" in the illustration is typically used to supply feed water to the evaporator, to supply the operating medium used in the removal of brine, and to supply the operating medium used in the removal of air and non-condensable gases. However, it does not supply the operating medium used in the removal of the distillate, as that function is typically performed by a separate system. The other answer choices (A, C, and D) are incorrect because they do describe functions of the water supply through item "P" in the illustration.