Not many people know that a vehicle's water pump has a weeping hole. There are two holes in the casting of the water pump, which are called vapor holes. The top row hole acts as an air vent that allows air to evacuate the casting system and prevents a build-up of humidity around the bearing.
It also takes advantage of atmospheric pressure to keep the seal intact. The bottom weep hole is present to allow any fluid that collects around the pump to drain out. This protects the integrity of the bearings.