Preheat the oven to 325 degrees F. Spray three 8-inch round cake pans with nonstick spray. (You can also use four 6-inch pans). Line the bottom of each pan with parchment paper, then spray the pans again.
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.
Pour the batter into the prepared pans (about 15 to 16 ounces in each) and bake for 22 to 25 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.