Bring the water to a boil in a large saucepan. Add the wild rice, cover and cook over moderate heat until tender, about 1 hour. Drain well.
Meanwhile, preheat the oven to 350°. Spread the hazelnuts on a rimmed baking sheet and toast for 15 minutes, or until fragrant. Transfer the nuts to a kitchen towel and let cool, then rub off the skins. Coarsely chop the nuts.
In a large, deep skillet, cook the bacon over moderate heat until crisp, about 8 minutes. Drain the bacon on paper towels. Pour off all but 2 tablespoons of the bacon fat from the skillet. Add 2 tablespoons of the butter and the leeks, celery and thyme. Season with salt and pepper and cook over moderate heat until the leeks are tender, 7 to 8 minutes. Add the wild rice, season with salt and pepper and cook just until warmed through.
Stir the toasted hazelnuts, the remaining 1 tablespoon of butter and the parsley into the wild rice, sprinkle in the bacon and serve.
Make Ahead: The recipe can be prepared through Step 3 and refrigerated for 3 days. Reheat the rice and add the hazelnuts and parsley before serving.