Combine the flour, sugar, cocoa, baking soda, baking powder and salt in the bowl of your stand mixer fitted with the paddle attachement and mix on low speed until combined.
In a separate bowl, whisk together the buttermilk, oil, eggs, water and vanilla.
With the mixer on low speed, slowly add the wet ingredients to the dry ingredients and mix until combied. Scape the sides and bottom of the bowl and mix a little longer to make sure everything is fully combined.
Add the batter to the third prepared pan. Use a kitchen scale and weigh each pan to make sure they are equal weight. If you don't have a kitchen scale eyeball it the best you can.
Bake the three cakes for 30 minutes and then check the doneness of each cake with a tooth pick. Continue baking each cake until the toothpick comes out clean. The three cakes may not bake at the same rate so keep a close eye on them.
Let the cakes cool in their pans for about 10 minutes then transfer to a wire rack to fully cool. Once cooled, use a large serrated knife or cake leveler to level each cake to the same height.