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Obviously, the temperature of water does not affect its chemical composition. At least not in the ranges we are likely to drink it in. Yet it is clearly far more pleasant and refreshing to drink cool water than it is to drink tepid or warm water.

Is there actually any difference to the organism or is this just a matter of perception? Is cool water somehow more efficient at rehydrating a cell? In any case, surely by the time water reaches individual cells it will have warmed up to body temperature.

So, what, if any, is the difference between drinking cool and warm water in terms of its effect on the human (or other animal) body?

Extra bonus for explaining why the taste of water changes when it is cold.

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However, on a hot day an hot drink will make you less thirsty than a cold one. – nico Jan 24 '13 at 18:19
    
Care to elaborate @nico? Are you saying that having a drink will make you thirsty? – terdon Jan 24 '13 at 18:38
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@terdon: no, I am saying that a hot drink will make you feel less thirsty on the long run. For instance we always bring hot tea when hiking in summer, even if it's quite hot. It's a matter of temperature difference, like having a hot shower in summer, you'll feel way more refreshed then after a cold one. – nico Jan 24 '13 at 19:47
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@terdon: If your drink is cold, your body has to heat the drink up to body temperature. This consumes energy, which leads to a higher body temperature, which leads to sweating. The net fluid balance can probably be negative. :-) That's why desert natives drink hot sweet tea. – Martin Schröder Jan 25 '13 at 18:09
    
@MartinSchröder, yes I understood from Nico's answer. That makes sense. It does not, however, answer the question. Indeed it contradicts it :). Why do we feel more refreshed when drinking cold water? Is it just a question of perception restricted to those surfaces that come directly into contact with the water (mouth, throat etc) or is there a deeper physiological reason as well? – terdon Jan 25 '13 at 18:34
up vote 8 down vote accepted

Short answer: Cold is pleasant only when your are not already freezing and cold might satiate thirst better because it acts as enhancer of the "water intake flow meter".


Is cold water more tasty than warm water? No, it is actually the reverse as detailed in my footnote.

Cold is pleasant when your body is over-heating and definitely not if you live naked in the North Pole. Over-heating means sweating which means you loose water and therefore feel thirsty faster. Yet drinking cold water will not rehydrate the body more than warm water and drinking water has only a very small impact on the body temperature. So why do we like it?

A study was actually conducted on the subject and answers most of your questions. Here the reference.

The temperature of the body will indeed not change.

cold stimuli applied to the mouth (internal surface of the body) do not appear to impact on body temperature and are not reported to cause any reflex shivering or skin vasoconstriction that influence body temperature.

As you pointed out, the temperature of the ingested water will not affect the overall hydration of the body as cells are rehydrated mostly via the blood stream and the blood temperature will not be affected. Someone could argue that, at identical volumes, cold water (above 4C) contains more molecules (i.e. is denser) than warm water but this difference is likely very slim.

In this paper they also define "thirst".

Thirst is a homeostatic mechanism that regulates blood osmolarity by initiating water intake when blood osmolarity increases

The problem is that it takes some time before the water reaches the blood stream, and therefore you need a feedback mechanism that tells you to stop drinking independently of the blood's osmolarity. This is where cold might play a role.

The cold stimulus to the mouth from ingestion of water may act as a satiety signal to meter water intake and prevent excessive ingestion of water

The picture would then be the following enter image description here

In essence, a cold sensation is pleasant in warm weather, both on the skin and in the mouth, and it apparently helps in reducing thirst by being some kind of an enhancer of the "water intake flow meter".


Footnote

Reading the comments I just want to clarify some points.

The 5 basic tastes (sweet, salty, bitter, sour and umami) are very distinct from taste sensations (pungency, smoothness, cooling to name a few). The main difference is that taste and "sensation" signals use completely different paths to reach the brain - namely, the facial and glossopharyngeal nerves for the former and the trigeminal nerve for the latter.

Is the temperature affecting basic taste perceptions? The answer is yes. How this happens is quite simple if you understand the fundamental concepts of molecular taste perception. Essentially the temperature affects the response of the receptor TRPM5 which is the main player in depolarizing taste receptor cells in the papillae. To put it simply, higher temperatures provoke a greater perception for taste, and this is not only in term of perceived taste but really modifies the amplitude of the response at the molecular level. As an example this is why ice cream does not taste sweet when frozen but only after it melted in the mouth or on the tongue.

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you are absolutely correct. It is the same if you live naked on the North Pole - you will find warm water more pleasant than cold. :) However please do note that stimuli to the mouth may not affect body temperature but stimuli to the stomach (i.e. almost core of the body) WILL affect body temperature. – mathgenius May 7 '15 at 12:39

I think it's because we are more often thirsty in a warm/hot/dry environment.
Since almost all of us have a house with a household furnace creating that warm/dry environment.

Thus cold water would be more refreshing since it also cools us off a bit.
I doubt that people that are on a north-pole expedition would still prefer that cold drink over a warm one.

This link contains a lot of information on this topic:
http://chestofbooks.com/health/nutrition/Dietetics-4/Temperature-And-Digestion.html

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Here's an armchair evolutionary explanation. In nature, running water tends to be cold whereas tepid water tends to be lukewarm. And for reasons having nothing to do with temperature, running water tends to contain less harmful bacteria. Therefore, our ancestors who preferred to drink cold water over lukewarm had an evolutionary advantage over those who preferred the opposite.

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In addition to cultural preferences and psychological factors, there may be some evolutionary basis in this.

Cooking food is a relatively new development and unique to the Homo spp. line. It makes sense that the tongue/mouth may be more sensitive to cooler temperatures than warm temperatures, given the amount of actual exposure it is given to sunlight and/or objects (across all species).

This is perhaps supported by the concentration of various receptor channels, TRPV1-4, TRPA1 and TRPM8, which are each sensitive/activated across various temperature ranges. TRPV3 operates through a range close to body temp. and has been associated with taste perception. One could hypothesise that in the mouth there is a greater concentration of cold-sensitive channels (such as TRPA1 and TRPM8) than warm ones, thus cold is perceived more readily and the addition of 'taste' channels (TPRV3) may contribute to the preference for cool water over say luke warm/room temp. water. This thinking falls down when we think of the amount of hot food we eat and can of course taste, in addition to the many studies conducted on taste perception, however this entire answer is very rudimentary.

I haven't found literature detailing the relative proportions of said channels, however, this makes for an interesting read: http://www.mnf.uni-greifswald.de/fileadmin/Zoologisches_Museum/Hildebrandt/Dokumente/schepers10.pdf

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Welcome to se.biology! Got scooped :). You should maybe modify slightly you answer to introduce TRPA1 and TRPM8 as the cold sensors. TRPV3 senses temperature closer to 37C and TRPV1 noxious heat. I might also just post an alternative answer. – cagliari2005 Mar 21 '15 at 19:33
    
Slightly modified (and hopefully correctly!). Perhaps you might be able to offer a much more comprehensive answer, though. – user15037 Mar 21 '15 at 20:06
    
Ah, so you're suggesting that the difference in taste is down ti the relative concentrations of these receptors, right? OK, any ideas on why one would feel more refreshing (which, presumably, translates to more hydrating) than the other? – terdon Mar 22 '15 at 12:56
    
@terdon I would be hesitant to offer anything concrete re: taste. I was trying to suggest that there might be a difference in concentrations, maybe weighted towards more cold-sensing receptors (TRPM8) rather than warmth-sensing receptors (TRPV1). The activation of TRPM8 by cold water could induce a more refreshed feeling by association - it is well known to be activated by menthol. This is a leap, but perhaps these pathways stimulate recollection of the feeling after your brush your teeth, use mouthwash, chew gum etc., often one of being clean, refreshed, or fresher. – user15037 Mar 22 '15 at 17:24

The organism as a thermodynamic machine does need a coolant. The more difference in temperature the more efficiently thermal machine can use energy. Also in all processes in organism it is produced excessive thermal energy, which should be removed.

Thus colder water and air are pleasant.

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