Heat 1/4 cup of the olive oil in a large skillet over medium-high heat; cook onions until soft, about 5 minutes. Add the rice; cook, stirring until rice begins to color. Cover; lower heat to low. Cook 5 minutes. Stir in the water, dill, pine nuts, salt and pepper, simmer 5 minutes. Let cool.
Place a heaping teaspoon of the filling in the center of each grape leaf with the shiny surface down. Fold the sides of the leaf over the filling; roll up loosely (the rice will swell when cooked). Place rolls in layers in a Dutch oven.
Sprinkle with lemon juice. Add remaining 1/4 cup of olive oil and 1 1/12 cups hot water. Place a heatproof plate over the rolls to prevent them from opening. Cover; simmer over low heat 1 hour. Let cool in the pan; refrigerate until ready to serve.