Increasing daily water intake by 3 L/day for one week does not reduce circulating arginine vasopressin or improve glucoregulatory health in healthy adults, as evidenced by unchanged fasting glucose and insulin levels despite a 15% reduction in copeptin.

When arginine vasopressin levels rise, it binds to receptors on pancreatic alpha cells, causing them to release more glucagon. Glucagon signals the liver to break down stored glycogen into glucose and release it into the blood. This raises blood sugar without changing insulin levels or how the body uses glucose. When water intake increases, arginine vasopressin drops, glucagon falls, and liver glucose output slows, but blood sugar stays the same because other systems balance the change.