Preheat the oven to 350°F. Lightly grease 2 9x5-inch loaf pans or 5-6 mini loaf pans.
In a medium mixing bowl, whisk together the flour, baking soda, baking powder, pumpkin pie spice, and salt until evenly combined.
In a large mixing bowl, whisk together the sugar, oil, eggs, pumpkin, and water until smooth.
Add the dry ingredients to the wet in 2-3 additions, mixing gently after each just until no streaks of flour remain. Do not overmix.
Divide the batter evenly among the prepared loaf pans, filling each about 2/3 to 3/4 full.
Scatter the pepitas on top of the batter if desired.
Bake until the tops are domed, browned, and slightly split, and a toothpick inserted in the center comes out clean, about 55-65 minutes for standard-size loaves or 45-55 minutes for mini loaves.
Remove from oven and let the loaves cool in the pans on a wire rack for 5-10 minutes.
Run a thin knife around the edges, then carefully remove the loaves and return them to the rack to cool completely, 30–60 minutes.
Once cool, serve or store in an airtight container.