Spread out the sweet potatoes in an even layer in a 9x13-inch casserole dish. Pour the water into the dish and cover with aluminum foil. Bake for 25 minutes, or until the sweet potatoes are just tender. Allow to cool slightly, then carefully pour as much of the water out of the dish as you can. Set aside, but do not turn off the oven.
During the last few minutes of baking, set a small saucepan over medium-low heat. Add the brown sugar, butter and five-spice powder and cook, stirring occasionally, until the butter is melted and the mixture starts to bubble. Remove from the heat and stir in the Sriracha sauce.
Pour the brown sugar mixture over the sweet potatoes and toss gently to coat. Sprinkle with salt to taste. Bake, uncovered, for an additional 10 minutes or until the potatoes are cooked through. Toss again before serving.