Bring chicken broth and water to a simmer in a saucepan (do not boil). Keep the broth warm over low heat.
Cut leek crosswise into thin slices. Heat oil in a large saucepan over medium heat. Add leek and celery, and sauté 2 minutes. Add rice and sage, and sauté 1 minute. Stir in wine, and cook 1 minute or until liquid is nearly absorbed, stirring constantly. Stir in 1/2 cup broth mixture, squash, and salt, and cook until liquid is nearly absorbed, stirring constantly. Add remaining broth mixture, 1/2 cup at a time, stirring constantly, and cook until each portion of broth mixture is absorbed before adding the next (about 20 minutes). Stir in Parmesan cheese, lemon juice, and pepper.
Excellent recipe, I've made ir several times and it's always a hit. You do need time to stand and stir, but it's worth it!