Preheat oven to 325°. Line a 9x9 pan with foil, or spray with non-stick cooking spray.
In a large mixing bowl, whisk together pumpkin, water, oil, eggs and pumpkin pie spice until blended. Mix in brownie mix and stir until blended. Mix in ½ of the package of chocolate chips. Spread in prepared pan.
Top batter with remaining chocolate chips and Halloween sprinkles.
Bake for 40–45 minutes, until edges pull away from the pan. Do not overbake.