A minor water leak prevention apparatus for a water inlet valve, in which a float is mounted on a regulation bar and received in a water container. The water container is mounted on a siphon tube. The siphon tube is formed with an air aperture. A counterweight buoyance switch is mounted on the water container. The counterweight buoyance switch has a counterweight water compartment having a lower end forming a water drain hole. The counterweight water compartment has an upper end to which a closure pressing plate is mounted. The closure pressing plate is opposite to the air aperture. The counterweight buoyance switch controls opening/closing of the air aperture. This arrangement allows water ingress through a water inlet valve to be stopped when minor water leakage occurs in a water tank.