Muscle glycogen stores are associated with the binding of 3–4 grams of water per gram of glycogen, and reduced glycogen levels lead to decreased intracellular hydration, which impairs the osmotic function of creatine as a cellular osmolyte.

Study: Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans

The study shows that when muscles store glycogen, they also store water—about 3 grams of water for every gram of glycogen—just like the claim says.

Study: Muscle glycogen depletion does not alter segmental extracellular and intracellular water distribution measured using bioimpedance spectroscopy.

The study found that even when muscle glycogen was low, the amount of water inside and outside muscle cells didn’t change, which goes against the idea that low glycogen dries out cells and makes creatine less effective.

Study: Creatine ingestion augments dietary carbohydrate mediated muscle glycogen supercompensation during the initial 24 h of recovery following prolonged exhaustive exercise in humans

The study found that creatine helped muscles store more glycogen after exercise, but it didn’t change muscle water levels or signs of cell swelling, which means water wasn’t being pulled in as the claim suggests.