Place biscotti in a food processor; process until coarsely ground. Place crumbs in a bowl; set aside.
Place chocolate syrup in a bowl; dip rims of 4 coffee mugs in syrup, and then in biscotti crumbs to coat rims; set mugs aside.
Add water, coffee, condensed milk, and 1/2 cup whipped topping to chocolate syrup; stir well. Pour into prepared coffee mugs; top each with 1 tablespoon whipped topping. Serve immediately.