Why does your belly bloat after one gallon of water?

Answer 1

because water can't be compressed, so your belly has to expand to accommodate the new volume.

Answer 2

Drinking a gallon of water in a short period of time can overwhelm the stomach's capacity to hold liquids, leading to bloating. The excess water can also disrupt the body's electrolyte balance and cause the stomach to expand, giving the sensation of bloating.