In a 4-quart heavy saucepan heat butter over medium heat until melted. Add onion and garlic; cook about 3 minutes or until tender, stirring occasionally. Add rice; cook and stir for 2 minutes. Carefully add wine; cook and stir until liquid is absorbed. Stir in snipped sage.
Meanwhile, in a large saucepan bring the water and the broth to boiling; reduce heat and simmer. Slowly add 1 cup of the broth mixture to rice mixture, stirring constantly. Continue to cook and stir over medium heat until most of the liquid is absorbed. Add another 1 cup of the broth mixture, stirring constantly. Continue to cook and stir until most of the liquid is absorbed. Add enough of the remaining broth mixture, about 1 cup at a time, cooking and stirring just until rice is tender but firm and risotto is creamy.
Stir in pumpkin and the 1/2 cup shredded cheese. Cook about 1 minute or until heated through, stirring occasionally. If desired, top each serving with shaved cheese and sage leaves.