Abstract: A water well filter device and a method for preventing airborne microorganisms from entering into a water well are disclosed. The water well filter device of the present invention contains a microorganism filter element having sufficiently small pore sizes to stop microorganisms from passing through. The water well filter device can further contain a pre-filter, a vacuum relief valve, or both. The method for preventing airborne microorganisms from entering into a water well involves connecting the water well filter device of the present invention to an opening of the well that is otherwise sealed from open air.