For most everyday situations, cool water in the range of about 50–60 °F (roughly 10–16 °C) encourages you to drink more and stay better hydrated than ice-cold or warm water does. But “best” depends entirely on what you are trying to accomplish. If you are exercising hard in the heat, colder is better. If you are congested with a cold, hot water does something cold water cannot. The honest answer is that no single temperature is ideal for every circumstance, and the research behind each scenario is more interesting than a blanket recommendation.
Cool Water Encourages You to Drink More
The single biggest factor in staying hydrated is simply drinking enough, and water temperature influences how much you voluntarily consume. A study of dehydrated taekwondo athletes tested water at three temperatures: cold (about 5 °C), cool (about 16 °C), and warm (about 37 °C). Cool water at 16 °C led to the highest voluntary intake, and those athletes had the lowest fluid deficit afterward. Cold water, despite what many people assume, did not encourage more drinking and did not improve hydration status compared to the cool option.1PubMed Central. Water temperature, voluntary drinking and fluid balance in dehydrated taekwondo athletes A separate experiment looking at post-exercise rehydration found the same pattern: water at 16 °C prompted higher intake while also keeping sweating lower than ice-cold water did, which together produced a better net hydration state.2PubMed Central. The effect of water temperature and voluntary drinking on the post rehydration sweating
The reason cool water wins seems to be straightforward palatability. Ice-cold water can feel sharp on the throat and trigger an urge to stop drinking sooner. Warm water is less refreshing in a hot environment. Cool water is comfortable to swallow in larger quantities without either extreme. If your main goal is just to stay well-hydrated throughout a normal day, a glass of cool tap water or lightly chilled water from the fridge is the practical winner.
How Water Temperature Affects Your Stomach
Cold water slows down your stomach. In a controlled trial that compared water at 2 °C, 37 °C, and 60 °C in healthy young men, cold water significantly reduced the frequency of stomach contractions compared to both warm and body-temperature water. That reduced motility was also linked to lower food intake at the meal that followed.3PubMed Central. The effects of water temperature on gastric motility and energy intake in healthy young men An older study found a similar trend: cold drinks appeared to empty from the stomach more slowly than drinks served at body temperature, with the initial rate of gastric emptying being significantly slower for the cold drink.4Gut. Effect of meal temperature on gastric emptying of liquids in man
What does this mean practically? If you are eating a meal and want your stomach to process it at a normal pace, room-temperature or warm water is a reasonable companion. If you are trying to eat less at a meal, a glass of cold water beforehand could modestly blunt your appetite by slowing gastric contractions. The effect is real but modest, so do not expect cold water to be a meaningful weight-loss tool on its own.
Cold Water and Exercise in the Heat
This is the one scenario where cold water has the clearest advantage. When you exercise in hot conditions, your core temperature rises and your body works hard to dissipate heat. Drinking cold water or ice slurry during exercise helps cool you from the inside, and the performance benefits are well supported. A systematic review concluded that cold water or ice slurry ingestion during exercise is an effective and practical way to improve endurance performance in the heat.5PubMed Central. Does Cold Water or Ice Slurry Ingestion During Exercise Elicit a Net Body Cooling Effect in the Heat?
Pre-exercise ice slurry ingestion (drinking a flavored slush at around 0 °C before working out) has also been studied. A scoping review of eleven studies found that more than half reported significant decreases in core body temperature and significant improvements in exercise performance when athletes drank ice slurry about 30 minutes before activity.6PubMed Central. The Effects of Pre-Exercise Ice-Slurry Ingestion on Thermoregulation and Exercise Performance of Highly Trained Athletes: A Scoping Review The mechanism is straightforward: cold fluid in your gut absorbs heat from surrounding tissue, temporarily lowering your internal temperature and giving you a larger thermal buffer before you overheat.
There is a trade-off, though. Cold fluid triggers receptors in your abdomen that reduce sweating independently of your actual core temperature.7Sports Science Exchange. Cold Water and Ice Slurry Ingestion for Reducing Body Temperature During Exercise in the Heat Less sweating means less evaporative cooling from the skin, which partially offsets the internal cooling you gain from the cold drink. On balance, the net effect still favors cold water during exercise in the heat, but it is not as large as the raw calorie-math of warming cold water to body temperature might suggest.
What Cold Water Does to Your Heart Rate and Blood Pressure
Drinking cold water produces a measurable cardiovascular response that most people never notice, but that could matter for some. In healthy younger and older adults, blood pressure spiked significantly during the act of drinking cold water. Older adults saw systolic blood pressure jump by about 40 mmHg with cold water and nearly 50 mmHg with cold carbonated water, compared to about 22 mmHg with room-temperature water. Younger adults showed a similar pattern at somewhat lower magnitudes.8PubMed Central. The Pressor Response to the Drinking of Cold Water and Cold Carbonated Water in Healthy Younger and Older Adults These spikes are transient, happening during the act of drinking itself, but a 40-point systolic swing could be concerning for someone with poorly controlled hypertension or a history of stroke.
Cold water also shifts the balance of your autonomic nervous system. A study comparing ice water to room-temperature water found that ice water increased vagal (parasympathetic) activity, which in turn slowed heart rate.9PubMed. The effect of ice water ingestion on autonomic modulation in healthy subjects For a healthy person, this is harmless and might even feel calming. For someone with certain cardiac arrhythmias or autonomic disorders, the sudden vagal surge could theoretically trigger symptoms. The practical takeaway: if you have a known heart condition, drinking very cold water quickly is worth discussing with your doctor. For everyone else, it is a physiological curiosity with no real downside.
Hot Water for Congestion and Gut Motility
Hot water has a genuine edge when you are sick with a stuffy nose. A classic study measured nasal mucus velocity, which is how fast the mucus lining of your nose moves to clear out particles and pathogens. Sipping hot water increased mucus velocity from about 6.2 to 8.4 millimeters per minute five minutes after drinking. Cold water, by contrast, actually decreased it, dropping mucus velocity from 7.3 down to 4.5 mm per minute. The hot-water benefit returned to baseline after 30 minutes, but the cold-water impairment lingered as well.10PubMed. Effects of drinking hot water, cold water, and chicken soup on nasal mucus velocity and nasal airflow resistance If you are congested, hot water (or soup) is genuinely helpful for clearing your nasal passages, and cold water works against you.
Warm water also appears to stimulate gut motility after abdominal surgery. In a randomized controlled trial of patients who had undergone laparoscopic gallbladder removal, those who drank warm water in the early postoperative hours passed gas significantly sooner, at around 11 hours versus nearly 19 hours for the control group.11PubMed. The Effect of Warm Water Intake on Bowel Movements in the Early Postoperative Stage of Patients Having Undergone Laparoscopic Cholecystectomy: A Randomized Controlled Trial That is a specific clinical setting, but it aligns with the broader observation that warmth relaxes smooth muscle in the gut. If you deal with occasional constipation or sluggish digestion, warm water in the morning is a time-honored remedy that has at least some mechanistic support.
Swallowing Disorders and Esophageal Spasm
For people with normal swallowing, water temperature barely matters. But for people with esophageal conditions, it can matter a lot. In patients with achalasia (a disorder where the lower esophageal sphincter does not relax properly), iced water increased the resting pressure of that sphincter, making swallowing harder. Hot water did the opposite: it decreased resting pressure and improved the sphincter’s relaxation rate.12Journal of Neurogastroenterology and Motility. Response of Esophagus to High and Low Temperatures in Patients With Achalasia One patient even developed esophageal spasm after cold water.
A separate study using high-resolution manometry showed that cold water reduced esophageal contraction strength in healthy people and in patients with non-obstructive dysphagia. In achalasia patients, however, cold water had no such dampening effect, meaning their already overactive esophagus stayed just as tight.13PubMed Central. Effect of Cold Water on Esophageal Motility in Patients With Achalasia and Non-obstructive Dysphagia: A High-resolution Manometry Study If you have trouble swallowing or have been diagnosed with an esophageal motility disorder, warm or room-temperature water is a safer default. Cold water could make things worse.
The “Cold Water Burns Calories” Claim
You may have heard that drinking ice-cold water forces your body to burn calories warming it up, and technically that is true. But the actual numbers are tiny. A study measuring energy expenditure after drinking water cooled to 3 °C found an increase of only about 4.5% over an hour.14PubMed. Water-induced thermogenesis reconsidered: the effects of osmolality and water temperature on energy expenditure after drinking The researchers noted that this was well below the theoretical energy cost of warming the water to body temperature, suggesting that the body is efficient enough to largely absorb the cold without a big metabolic penalty. In practical terms, the extra calorie burn from drinking cold water throughout a day would amount to a handful of calories, less than what is in a single cracker. Drink whatever temperature you prefer; calorie burning is not a reason to choose cold.
Brain Freeze and Cold-Stimulus Headaches
That sharp, stabbing headache you get from gulping something very cold is called a cold-stimulus headache, and it is not limited to ice cream. Cold water consumed quickly can trigger the same sensation. Research confirms that the triggers and clinical features of cold-stimulus headache in children are similar to those in adults.15PubMed Central. Cold-Stimulus Headache in Children and Adolescents The pain comes from rapid cooling of the palate and the back of the throat, which causes blood vessels in the head to constrict and then rapidly dilate. It is harmless and passes within seconds to a couple of minutes, but it is extremely unpleasant. People who get migraines tend to be more susceptible. Sipping cold water slowly rather than gulping it avoids the problem entirely.
Why Your Plumbing Temperature Matters
Most conversations about water temperature focus on the glass in your hand, but the temperature of water sitting in your pipes affects what is growing in it. A study examining biofilm growth in drinking-water systems found that certain opportunistic pathogens grew more aggressively as water temperature increased. Two species began growing at 15 °C, another above 20 °C, and a fourth above 25 °C, with peak growth yield for most reaching its highest at 30 °C.16PubMed Central. Influence of Temperature on Growth of Four Different Opportunistic Pathogens in Drinking Water Biofilms The researchers warned that rising water-infrastructure temperatures, driven partly by climate change, could increase the pathogen load in drinking water.
This is not a reason to panic about your tap water. Municipal water treatment handles microbial risk before it reaches your home, and most healthy immune systems handle trace exposures without issue. But it does mean that water sitting stagnant in warm pipes, say in a building that has been unoccupied during a hot summer, could harbor more bacteria than freshly flushed cold water. If your tap has been sitting unused for days or weeks, letting it run cold for 30 seconds to a minute flushes out the stagnant, warmer water that sat in the pipes and reduces any microbial buildup.
Putting It Together by Situation
Rather than declaring a single champion temperature, here is what the research actually supports for specific scenarios:
- Daily hydration: Cool water around 16 °C (about 60 °F) encourages the highest voluntary intake and is the best bet for staying well-hydrated in normal conditions.
- Exercise in the heat: Cold water or ice slurry consumed before and during activity lowers core temperature and improves endurance performance.
- Nasal congestion: Hot water sipped slowly increases mucus clearance and helps open nasal passages. Cold water does the opposite.
- Digestive comfort: Warm or room-temperature water supports normal stomach emptying and gut motility. Cold water slows gastric contractions.
- Swallowing difficulties: Warm water relaxes the esophageal sphincter and is gentler for people with motility disorders. Cold water can provoke spasm.
- Heart and blood pressure concerns: Room-temperature water produces smaller blood-pressure spikes than cold water, which matters most for older adults and people with cardiovascular conditions.
One temperature that almost never makes sense is scalding hot. Water above about 65 °C (149 °F) has been classified by the International Agency for Research on Cancer as a probable carcinogen for esophageal cancer when consumed habitually. The risk comes from repeated thermal injury to the esophageal lining. If you drink tea or coffee, letting it cool until you can sip comfortably without flinching is a sensible habit. The studies reviewed here used “hot” water in the 50–60 °C range, warm enough to provide the beneficial effects on mucus clearance and sphincter relaxation without crossing into tissue-damage territory.