To prepare the brine, bring half of the water to boil and add the sugar, kosher salt, and garlic powder. Stir frequently until the sugar and salt have dissolved, then allow the brine to cool down.
Once the mixture is at room temperature, add the rest of the water, the lemons, and the mandarins. Refrigerate to cool the mixture down at 40° F or below before adding the chicken.
Remove any giblets that may be inside the chicken cavity, and discard (I like to keep and use them for my stock). Add the chicken in the brine, cover, and refrigerate overnight.
Once brining is done, rinse the meat under cold water for about 5 minutes to remove any excess salt, then pat dry with a paper towel.