West Kill Mountain stands within the watershed of the Hudson River, which drains into New York Bay.
The north slopes drain into the West Kill, thence into Schoharie Creek, the Mohawk River, and the Hudson River.
The southeast slopes of the mountain drain into Hollow Tree Brook, thence into Stony Clove Creek, Esopus Creek, and the Hudson River.
The southwest slopes of West Kill Mountain drain into the Broadstreet Hollow stream, thence into Esopus Creek.
