Waterman, an insurance salesmen, was inspired to improve the early fountain pen designs after destroying a valuable sales contract with leaky-pen ink. Waterman's idea was to add an air hole in the nib and three grooves inside the feed mechanism. A fountain pen mechanism is composed of three main parts. The nib, which has the contact with the paper. The feed or black part under the nib controls the ink flow from the reservoir to the nib.
All fountain pens contain an internal reservoir for ink.
The different ways that reservoirs filled, proved to be one of the most competitive areas in the pen industry. The earliest 19th century fountain pens used an eyedropper, by 1915 most pens had switched to having a self-filling soft and flexible rubber sac as a ink reservoir. To refill these pens, the reservoirs were squeezed flat by an internal plate, then the pen's nib was inserted into a bottle of ink and the pressure on the internal plate was released so that the ink sac would fill up drawing in a fresh supply of ink. An external button connected to the internal pressure plate that flattened the ink sac when pressed. Walter Sheaffer patented the lever filler in 1908.