Preheat oven to 350 degrees F.
Lightly spray 3 9-inch cake pans with baking spray and set aside. For best results, add parchment paper on the bottom and spray with baking spray on top.
In a large bowl, combine the flour, baking soda, baking powder, and salt. Stir and set aside.
In another large bowl, using a standing mixer, cream the butter, shortening, and sugar until light and fluffy. Add the eggs one at a time. Beat in vanilla extract until combined. Stop a few times to scrape the sides and bottom of the bowl.
Gradually beat in ⅓ of the flour mixture until combined. Add the water, buttermilk and oil. Beat to combine.
Beat in another ⅓ of the flour mixture and beat in the milk. Add the remaining flour mixture and beat to combine.
Stir in the sprinkles.
Divide the batter between the prepared 3 cake pans.
Bake in the oven for 25-30 minutes or until a toothpick comes out clean.
Allow the cakes to cool completely before assembling.