Measure water into a 2-quart glass measuring cup or other heatproof container. Sprinkle gelatin over the water and stir until evenly moistened. Let stand until the gelatin is soft, about 3 minutes.Advertisement
Meanwhile, combine juice and sugar in a medium saucepan and bring to a boil over medium-high heat. Gradually stir into the gelatin mixture. Continue to stir until the gelatin is completely dissolved, 1 to 2 minutes.
Refrigerate the mixture until slightly thickened and syrupy, 2 1/2 to 2 3/4 hours. Pour a 1-inch layer of it into a 1 1/2-quart glass serving dish. Gently arrange half the raspberries in a single layer on top. Return both containers to the refrigerator for 15 minutes, then pour another layer of gelatin over the berries. Top with the remaining berries and pour the rest of the gelatin mixture over them.
Refrigerate until completely set, about 2 hours more.
Make Ahead Tip: Cover and refrigerate for up to 3 days.