Preheat the oven to 350 degrees F. Line a 12-cup cupcake tin with cupcake liners and set aside.
Whisk together the flour, sugar, pumpkin pie spice, salt, baking powder and baking soda in a large bowl. Whisk together the eggs, buttermilk, pumpkin, oil, vanilla and 3/4 cup water in a medium bowl. Add the wet ingredients to the dry ingredients and stir to combine.
Pour the batter evenly into the cupcake tin and bake until a toothpick inserted in the center of a cupcake comes out clean, 28 to 32 minutes. Let cool in the pans for 10 minutes, then turn onto a wire rack to cool completely.