Some say its only useful property in this regard is that it delivers a jolt of energy to the system if the water is cold and consumed quickly; while others argue in favor of warmer water and some dismiss the entire notion as an old wife's tale.
"Some people who suffer from constipation have benefited from drinking a glass of water first thing in the morning, and they have kept this up for a long time. But other patients have seen no change in their condition," said Lee Bong-eun, a physician at Pusan National University Hospital.
"In theory, though, your intestines are not very active when you awake on an empty stomach, so a glass of water could stimulate your digestive tract and soften up the contents."
But Lee said the effects may vary from person to person. He also advised those who have benefited from the practice to switch over to consuming lukewarm water. "Gulping down ice-cold water on an empty stomach could actually do more harm than good to your digestive tract," he added.