thirstThirst is the basic need or instinct of humans or animals to drink. It arises from a lack of fluids and/or an increase in the concentration of certain osmolites such as salt. If the water volume of the body falls below a certain threshold, or the osmolite concentration becomes too high, the brain signals thirst. The osmolite concentration in the blood is measured with specialized sensors in the hypothalamus, notably in two circumventricular organs that lack an effective blood-brain barrier, the organum vasculosum of the lamina terminalis and the subfornical organ. These areas project to the supraoptic nucleus and paraventricular nucleus, which contain neurons that secrete the antidiuretic hormone, vasopressin, from their nerve endings in the posterior pituitary, but also project to other hypothalamic areas, including especially the median preoptic nucleus to trigger thirst. Continuous dehydration can cause myriad problems, but is most often associated with neurological problems such as seizures, and renal problems.

Excessive thirst, known as polydipsia, along with excessive urination, known as polyuria, may be an indication of diabetes. Angiotensin II is a hormone which is a powerful dipsogen (ie it stimulates thirst) which acts via the subfornical organ.

According to most experts, humans need 8-10 servings of about 8-ounces of water per day to be fully hydrated, though this does vary according to temperature, movement, physical size etc. 8 servings are widely regarded as the minimum just for the body to function correctly. Water is essential to the general function of the human and all animal bodies. Water also helps the human body break down fat and burn it off faster. Most experts agree that it will also help wrinkles disappear by hydrating your skin, giving you a healthier appearance. Hydration through water is also essential to maintain and keep the digestive tract in order . Some experts also state that if humans do not get at least the minimum amount of H2O per day then the digestive system will not function properly. Water not only helps flush distructive toxins from the body, but helps prevent and indeed heal urinary tract infections.

In the example of pure water hydration, iced tea, coffee, soft-drinks, etc are not a replacement for pure water. In fact, caffinated beverages actually work as a diuretic, causing your body to get rid of its fluids, causing the body to need more water. According to experts, a good rule of thumb to follow is to drink about four ounces of water for every hour you are awake, though again this does vary according to circumstances. According to an unknown source:

"If you are engaged in some kind of hot activity (something that makes you sweat), you'll need to drink more"

Most experts agree that for the human body it is beneficial to hydrate yourself with smaller amounts of water and allow your body to absorb what it needs over a certain time span. Some health experts state that the human body doesn't always let you know when it needs water, so it can be best to stick to a regular drinking schedule, thirst or not. Medically however, a sure indicator to watch for that you aren't getting enough water is the color of your urine: if it has any colour at all, then you probably need more water (though do check with a doctor if you unsure).