Place water in a heavy based sauce pan over medium heat. Allow water to come to a slow simmer. Slowly pour polenta into water while whisking to combine. Reduce heat to as low as possible. Stir polenta occasionally with a wooden spoon for 40 to 45 minutes. Polenta is cooked when it comes away from the sides of the pan. Stir in salt, pepper, butter, parmesan, mascarpone and keep warm.