Heat oven to 350℉/177℃.
Spray an 8-inch x 3-inch round cake pan with baking spray. Set aside.
In a medium bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt. Set aside.
Place bittersweet chocolate in a medium microwave safe bowl.
Microwave in 15 second increments, stirring well after each, until chocolate is melted and smooth. Set aside.
In a large bowl, whisk together eggs, milk, oil, vanilla, and water.
Mix in melted chocolate.
Add dry ingredients to chocolate mixture.
Whisk until smooth.
Pour into prepared pan.
Bake for 55 minutes, or until cake tests done.