Traditional Chinese Medicine (TCM): In TCM, the body's health depends on a balance of yin (cold) and yang (hot) energies. Ingesting cold food or drinks, especially 凉水, is believed to introduce “coldness” (寒气, hánqì) into the digestive system. This can disrupt the body's balance, slow down metabolism, and is considered particularly harmful for women (especially during menstruation) and anyone who is sick or has a weak constitution. Warm or hot water, in contrast, is seen as neutral or beneficial, aiding digestion and circulation.
Historical Hygiene: For centuries, China lacked modern water purification infrastructure. The most reliable way to ensure water was safe to drink was to boil it, killing harmful bacteria and pathogens. This practice became a deeply ingrained habit. Therefore, 凉水 historically carried the connotation of being “unboiled” and potentially unsafe tap water (生水, shēngshuǐ). Boiled water that has cooled down is called 凉开水 (liáng kāishuǐ) and is considered safe.
Comparison to Western Culture: This contrasts sharply with Western norms, where ice water is the standard offering in restaurants and is seen as refreshing and hydrating. In the U.S., you have to ask for “no ice” or “hot water,” whereas in China, you almost always have to specifically ask for 凉水 or 冰水 (bīngshuǐ). This simple difference in beverage temperature is a classic example of “culture shock” for many travelers.