Bring water and stock to a boil, then reduce heat to low to keep warm.
In a large skillet, heat oil and butter over medium to medium high heat. Add onions and saute 3 minutes. Add arborio rice and saute, 2 or 3 minutes more. Add wine or sherry and allow liquid to absorb, 1 minute. Add 1/2 the stock or broth and reduce heat slightly. Simmer, stirring frequently until liquid is absorbed, then add more liquid, a few ladles at a time. When liquid cooks out, ladle in a bit more.
When risotto has cooked almost to al dente, about 18 minutes, fold in spinach, basil and parsley. Season risotto with nutmeg, salt and pepper and stir in any remaining broth. Risotto will cook 22 minutes, total. Stir in cheese and serve immediately.