Thirst can be a poor way of monitoring of your water needs. You can lose your thirst sensation and the critical perception of needing water. No longer recognizing a water need (unless very dehydrated), you can become gradually, increasingly, and chronically dehydrated with increasing age. A "dry mouth" may be a late sign of dehydration.
Water has many functions in your body. Water:

Here are some interesting facts:
Pain may be a warning of localized thirst; that is, the pain signal may be a warning of dehydration in that specific area (a regional thirst), for example low back pain, migraine headache, joint pain, and angina. Chronic dehydration may contribute to a reduction in lymph flow, which in turn may contribute to or cause varied problems.
Obvious signs of dehydration include: crinkled skin, dry mouth, excess thirst or absence of urination for over six hours.
It is a common error to substitute tea, coffee, caffeine-containing soft drinks, or alcohol-containing beverages for water. Do not consider alcoholic beverage, soda, coffee or tea as an equal substitute for water. Caffeine and alcohol act as diuretics, further increasing your water needs.

Remember that approximately half of your daily water intake comes from the food that you eat, so you only need to drink around half of your suggested requirement directly.
Calculate your overall daily need by taking your weight in kilograms (or your weight in pounds divided by 2), in ounces per day. For example, 140lbs / 2 = 70oz; 70oz / 8 = about 9 cups per day.
It is recommended by some that you not drink water with meals, unless you need to. Other doctors believe that the stomach needs a certain consistency to do its job and if we don't drink enough with our meals the stomach pulls water from the blood stream; if we drink too much with our meals the excess water simply gets absorbed. The logical recommendation, therefore, is to try both and see what works best for you.
Good times to drink water are on rising, at least 1⁄2 hour before meals and 2-3 hours after, and before bed. You need more if the temperature is hot and if you exercise. A general rule is to add an extra 2 glasses per day for every 5°F over 85°F if you are at rest, and more if you exercise.
We recommend that you read Your Body's Many Cries for Water by Dr. Batmanghelidj, MD. It may be available from your local library. If purchased, you may be able to help others you think of while reading it!
"In my professional and scientific view, it is dehydration that is the biggest killer, more than any other condition you could imagine. The different aspects and 'chemical idiosyncrasies' of each individual's body reaction to the same pattern of dehydration have received different professional labels and have been treated differently and ineffectively." Dr. Batmanghelidj, MD.
Adverse reaction to delayed meals
When we skip meals, we often also skip the drinks that go with the food. If your hydration status is already marginal, a delayed meal may be enough to trigger dehydration symptoms.
Angina
Dr. Bantmanghelidj, MD in his book Your Body's Many Cries for Water reports many cases of angina attacks being reduced by drinking adequate water.
Heartburn / GERD / Acid Reflux
Dr. Batmanghelidj, author of Your Bodies Many Cries for Water, believes that in the same way we have a "hunger pain" signal, we also have a "thirst pain" signal in the body, and that it is called dyspepsia (heartburn).
Lymphatic Congestion
Drinking plenty of water makes sure the body is well-hydrated and helps the lymphatic system do its job of flushing toxins and waste from the body.
Susceptibility To Hangovers
The most obvious source of headaches due to hangovers is dehydration caused when alcohol suppresses anti-diuretic hormone. This hormone normally orders the body to conserve water, but alcohol dulls the command, causing people to lose far more water to urination than they take in with the alcohol.
The body reacts to the open floodgates by borrowing water from other organs, such as the brain. As a result, the brain shrinks. While that may not cause pain by itself, the brain has a covering called the dura that is connected to the skull by pain-sensitive filaments. Deformation of the dura can cause the headaches that come with a hangover.
Gout / Hyperuricemia
Gout can be caused by dehydration and the use of diuretics such as coffee or alcohol.
Muscle Cramps / Twitching
Excess sweating or dehydration can deplete minerals in the body – minerals that are important for good muscle function, such as sodium, potassium, calcium, magnesium and phosphorus.
General Weakness
A loss of 4-5% of body weight of fluid decreases the capacity for hard muscular work by 20-30%.
Ulcerative Colitis
Dehydration occurs in patients with severe diarrhea as seen in ulcerative colitis.
Caffeine Intoxication
Dehydration may result from the increased urinary frequency brought on by caffeine.
Excess Protein Consumption
High protein intakes may lead to dehydration due to excessive urine output (related to ketone production).
(High) coffee consumption
Caffeine has a mild diuretic action and may thus worsen dehydration, except when taken during exercise. One study found that the difference between ingesting the same volume of a non-caffeinated sports drink and the same drink containing caffeine (25mg per 100ml) was that urine production after the caffeinated drink was significantly higher at rest by 31%. However, ingestion of caffeinated beverages during physical activity did not increase urine production and exacerbate dehydration. [International Journal of Sports Medicine. 18: pp.4046-4053, 1997]
Alzheimer's Disease
Due to older people's precarious homeostatic mechanisms they are much more prone than younger people to dehydration and electrolyte imbalances. This may induce a confusional state which may be mistaken for a dementing illness such as Alzheimer's.
Your body is a highly complex, interconnected system. Instead of guessing at what might be wrong, let us help you discover what is really going on inside your body based on the many clues it is giving.
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