Bring water to a boil in a medium saucepan; add rice and 1/2 teaspoon salt. Cover, reduce heat, and simmer 40 minutes or until liquid is absorbed. Remove from heat; uncover and cool to room temperature.
Heat oil in a large nonstick skillet over medium-low heat. Add leek; cook 10 minutes or until tender, stirring frequently (do not brown). Add garlic; cook 1 minute. Reserve 1/4 cup leek mixture; stir remaining leek mixture into rice. Stir parsley and next 7 ingredients (parsley through 1/8 teaspoon salt) into rice mixture. Add 1/8 teaspoon pepper.
Combine reserved 1/4 cup leek mixture, tomatoes, and 1/8 teaspoon black pepper in skillet; bring to a boil. Reduce heat, and simmer 10 minutes. Remove from heat.
Rinse grape leaves with cold water; drain well. Pat dry with paper towels. Remove stems; discard. Select 24 large leaves; reserve remaining leaves for another use. Spoon 1 rounded tablespoon of rice mixture onto center of each grape leaf. Bring 2 opposite points of leaf to center; fold over filling. Beginning at 1 short side, roll up leaf tightly, jelly roll fashion. Repeat procedure with remaining leaves.
Nestle stuffed grape leaves, seam sides down, in tomato sauce. Cover and cook over medium-low heat 20 minutes or until thoroughly heated.