Preheat the oven to 325 degrees F. Spray three 8-inch or four 6-inch round cake pans with nonstick spray, line with parchment paper, then spray the parchment paper as well. 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. Mix lightly until combined.
With the mixer on low speed, slowly add the wet ingredients to the dry. Scraping the bottom of the bowl with a rubber spatula, and mixing for 30 more seconds on medium-low speed.
Pour the batter into the prepared pans (about 15 to 16 ounces in each 8-inch pan or 10 ounces in each 6-inch pan) and bake for 25 to 30, until a toothpick comes out with a few moist crumbs on it.
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.