The stopcocks and shutoffs at the curb shall be covered with a standard cast iron box which shall be placed two feet inside the curb line in front of the premises supplied, and in all cases shall be set flush with the surface of the sidewalk or ground. The same shall be kept free from dirt or other obstacles that would interfere with the shutting off or turning on of water. Each house or building shall have a separate and distinct stopcock, located outside the premises, and on public right-of-way adjoining such premises.