Preheat your oven to 325 degrees F. Spray two 8-inch round cake pans with nonstick spray, line the bottoms with parchment paper and spray again. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, stir together the flour, sugar, cocoa, Oreos, baking soda, baking powder and salt.
In a medium size mixing bowl, whisk together the buttermilk, eggs, oil, vanilla and water.
With the mixer on low speed, gradually add the wet ingredients to the dry ingredients and stir until combined.
Scrape down the sides and bottom of the bowl and mix again on low for another 20 to 30 seconds.
Evenly divide the batter between the two pans and bake for 30 to 35 mintues, or until a toothpick inserted in the center of the cake comes out with just a few moist crumbs on it.
Remove the pans from the oven and cool in pans for about 15 mintues before inverting on wire racks to cool completely.
Before stacking this cake, use a cake leveler to divide each cake in half horizontally to create four layers.