The standard in the United States is to serve water and many other beverages ice cold. This is particularly true in the summer. People need to cool down and a cold drink is usually the best way to do that- or is it? In Traditional Chinese medicine the thought is that warm or cool beverages are better at cooling the body and quenching thirst than ice cold beverages.
The human body is a warm blooded system. In order to deal with excess heat the body dilates the blood vessels near the skin ( causing red flushed skin) and sweating. This process allows for evaporation of water on the skin, cooling the skin and blood to help regulate body temperature. The Traditional Chinese Medical view is that there is a flow of energy pumping heat out from the central core of the body to the extremities.
The introduction of ice cold beverages into the central core of the body would then cause the body to shift the direction of heat flow in the body. The digestion needs to maintain a warm temperature for the proper functioning of the digestion. If the stomach is cooled then the body needs to direct heat inwards to maintain internal heat. This runs counter to the natural cooling function of the body. This is also the reason why some people get headaches and stomach aches from drinking too much cold water too fast.
The Chinese herbal perspective is to utilize warm to cool water and beverages which rehydrate and enhance the ability of the body to pump out more sweat and cool the body naturally. The recommendation is also to utilize tropical fruits and melons which hydrate and cool the body. Green tea and mint are also useful because they have a functional dynamic of dispersing heat out of the body.
Most people use ice water and have never really thought about it. Many people can feel the difference when they switch to cool non-iced beverages to cool off. Some people are more sensitive to the cold beverages than others. Many people find that when they switch to cool and warm beverages to cool off, they quench their thirst more quickly with less water, and they often feel more energetic without the headaches and stomach upset that can come from iced beverages.