Place an oven rack in the center of the oven. Preheat the oven to 300 degrees F. Line 2 baking sheets with parchment paper or silicone mats. Set aside.
In a small bowl, combine the bittersweet chocolate and butter. Place the bowl over a pan of barely simmering water and stir occasionally until the chocolate has melted and the mixture is smooth.
In a medium bowl, whisk together the flour, cocoa powder, baking powder and salt.
In another medium bowl, whisk together the sugar, eggs, 2 tablespoons water and vanilla extract. Gradually add the dry ingredients and stir until thick and smooth. Fold in the melted chocolate. Stir in the chocolate chips. Using a cookie or ice cream scoop, scoop level 1/4 cupfuls of the batter onto the prepared baking sheets. Bake until slightly puffed and the tops begin to crack, 18 to 20 minutes. Allow the cookies to cool completely on the baking sheets and serve.