Preheat the oven to 360 degrees F. Spray three 8-inch or four 6-inch round cake pans with nonstick spray. Line the bottom of each pan with parchment paper, then spray the pans again. Set aside.
Combine the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with a paddle attachment and mix on low speed until combined.
In another bowl, combine the buttermilk, oil, eggs, water and vanilla.
With the mixer on low speed, slowly add the wet ingredients to the dry, scraping the bottom of the bowl with a rubber spatula.
Evenly distribute the batter into the prepared pans and bake for 16-18 minutes.
Cool in the pans for 10 minutes, then turn them out onto a cooling rack and cool completely.
Wrap in plastic wrap and chill until ready to use. You're still going to want to level your cake layers to ensure a completely even surface for frosting and stacking.