An adult living  in a temperate climate should drink at least 1.5 litres of water per day.

Water is very essential for life, and maintaining water level/hydration is important for physical and mental performance of anyone. People generally drink enough water, but for specific population groups, like the elderly, or while exercising, fluid intake (water, milk, juices, etc.) might become critical.

Dehydration may --- cause headaches, tiredness, loss of concentration, etc.

So, one should drink enough to balance water losses in the body. All water-containing drinks --  including fruit juices, soft drinks, tea, coffee, dilute alcoholic drinks such as beer, pure water, etc. --- can contribute to the total required for hydration.

See link for functions of water.

http://www.nestle-waters.com/healthy-hydration/water-fonctions-in-human-body

An adult living  in a temperate climate should drink at least 1.5 litres of water per day.

Water is very essential for life, and maintaining water level/hydration is important for physical and mental performance of anyone. People generally drink enough water, but for specific population groups, like the elderly, or while exercising, fluid intake (water, milk, juices, etc.) might become critical.

Dehydration may --- cause headaches, tiredness, loss of concentration, etc.

So, one should drink enough to balance water losses in the body. All water-containing drinks --  including fruit juices, soft drinks, tea, coffee, dilute alcoholic drinks such as beer, pure water, etc. --- can contribute to the total required for hydration.

See link for functions of water.

http://www.nestle-waters.com/healthy-hydration/water-fonctions-in-human-body

Don´t forget please the daily water produced in the body by burning digestion processes (about 300 ml) and the hidden water in solid nourishments (about 700 ml). 

The body is about 60% water, give or take.We’re constantly losing water from our bodies, primarily via urine and sweat. There are many different opinions on how much water we should be drinking every day.

The health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon. This is called the 8×8 rule and is very easy to remember.

However, there are other health gurus who think we’re always on the brink of dehydration and that we need to sip on water constantly throughout the day… even when we’re not thirsty.

As with most things, this depends on the individual and there are many factors (both internal and external) that ultimately affect our need for water.

http://authoritynutrition.com/how-much-water-should-you-drink-per-day/

For some of us in the tropics with daytime temperatures of 35 Celsius, we have to drink a lot of water.  Perspiration rate is high.  We drink about 3 to 4 liters of bottled water a day.  At home, I needed 2 water filters and the water is clean.  But at college, I have only 1 filter.  So I drink bottled water at college.  Subhash has described dehydration symptoms.

Theoretically water that enters the body is equal to water that is lost through excretion by the kidneys and through perspiration.  The water regulation of our body is controlled by ADH; see the link for the function of ADH.

http://www.abpischools.org.uk/page/modules/homeostasis_kidneys/kidneys6.cfm

I think the need for hydration is different for each individual. In my opinion I do not think it's a matter of weight. I also believe that every individual to own the metabolism due to its nature (emotions). Personally I weigh 79 kgs for a size of 172 cms. Keep you well my average water consumption during the winter is about 03 liters / day. In summer my average consumption 5-6 liters / day. Being a real emotional I often go to the bathroom to urinate. A good tip take in the morning on an empty stomach a glass of water or too cold or hot. This allows you to remove stones in the kidney.

Water leaves the body in many ways, categorized into either “sensible” water loss or “insensible" water loss depending on whether the loss can be perceived by the senses. “Sensible” water loss includes such processes as sweating and vomiting. “Insensible" water loss occurs mainly through the skin and respiratory tract.[15] In humans,

dehydration can be caused by a wide range of diseases and states that impair water homeostasis in the body. These include the following:

• External or stress-related causes
• Prolonged physical activity with sweating without consuming adequate water, especially in a hot or dry environment
• Prolonged exposure to dry air, e.g. in high-flying airplanes (5%–12% relative humidity)
• Blood loss or hypotension due to physical trauma
• Loss of fluid through weeping burns or other injury

SEE: http://en.wikipedia.org/wiki/Dehydration

As much as one can. Human body is such great design that excessive water is released from body it maintains the balance.  Water ensures that we do not suffer from kidney or acidity or digestion related issues. We are basically water based construction.

It seems to me that we should not set an absolute amount of consumption of water for an adult to be hydrated. For proper metabolism is fixed a certain amount but can vary from one adult of the same sex, same weight who live under the same climatic conditions. This infers that there other intrinsic factors that make the difference. Taking the same example except that they live in two different climates so their needs will be different in relation to extrinsic factors climatic factors

We should not try to hydrate our body with any other liquid, but water. Any sweet drinks will not substitute water. The second best drink is tea. Which, if I am not mistaken, will have the ability to hydrate one's body about 83% comparred to what water would do.

With very few exceptions, the food product contains a quantity of water not negligible.

Average water content in various foods (% of edible part)

FOOD

0 / oil, sugar

2-10 / biscuits, nuts (peanuts, walnuts, pine nuts), popcorn

10-20 / butter, flour, dried vegetables, honey, pasta

20-40 / cheese (parmesan, gruyere), bread, pizza

40-60 / Fresh cheese (dairy products), ice cream, cold cuts

60-80 / Meat, fish, eggs

> 80 / Fresh fruits, vegetables and vegetables, milk

The water balance is kept in balance by adjusting the output (by changing the volume of urine excreted) and through the control of income (changing the water intake).

At baseline, 60% of the daily loss of water occurs in the urine. The temperature rise and exercise do instead increase water loss through sweating and insensible perspiration.

The dehydration, even if modest, is a dangerous condition for the organism. A 7% decrease in total body water is sufficient to endanger the survival of the individual.

In general you should drink at least a liter and a half of water a day

Every time we drink water because we feel thirsty, it means you let our body dehydrate. We have to drink water for never feeling thirsty throughout the day and the urine should be colorless and ordorless.

You'll be surprised by reading the benefits of drinking water below.

• weight loss

Drinking water helps to reduce body weight as fat composition can be adverse. Drinking appetite and desire to eat you will stop. After you drink less. In addition, water has zero calories.

• Natural Remedies Headache

To eliminate headaches and back pain caused by dehydration, which helps. The main reason for the pain of the loss of water from the body.

• The younger you'll be refreshed skin.

When the water of your skin, you'll look younger. Water helps the skin tissue to be built again, moist skin and increase its elasticity.

• increased efficiency in the workplace.

Your brain is made up of a large volume of water. In addition to drinking water makes you feel better, you can be vigilant and concentrate better.

• Bdnytan activity increases.

Drinking water helps regulate body temperature, the more energy you feel when you are exercising and eating better muscles.

• assist in digestion and prevent constipation.

BMR drinking water because it helps in digestion. Fiber and water together and makes it easier to move your bowels.

• sprains and cramps less.

Water causes the body to fit your joints and muscles lubricated and you will have fewer cramps and sprains.

• less likely to get sick and not feeling well.

Drink plenty of water can resist the flu and other diseases such as kidney stones or around your heart. Of lemon juice for the treatment of respiratory and intestinal problems, rheumatism, arthritis pain and other benefits of water can also be used to increase the body's immunity.

• Eliminate fatigue.

Water that enters the body, it causes the toxins and waste products from the body and the body is washed out.

• good mood.

When your body feels good, you will feel the spirit of good will.

• Reduce the risk of cancer.

In relation to the digestion system, some research has shown that drinking large amounts of water, bladder and colon cancer risk decreases. Water concentration of carcinogenic cells at low urea and urea is also due to dilution. The contact time is reduced bladder coated urea.

Risk factors for dehydration

Anyone who lose large amounts of body fluids, the body will become dehydrated. But some people more than others with this problem are as follows:

1. Infants and Children

Most also have diarrhea. Diarrhea will cause dehydration.

2. The elderly

With increasing age, the more reasons you are more prone to dehydration:

- Your body's ability to maintain and preserve the water is low.

- Your thirst is slower, the later you realize your thirst.

- Less can respond to changes in temperature.

They also made the failure or neglect to eat well.

In addition to these problems, chronic diseases such as diabetes and dementia (dementia) and there were drugs in the elderly.

3. People with chronic diseases

Untreated or uncontrolled diabetes increases the risk of dehydration.

Other chronic diseases such as kidney disease and heart failure also increase the risk of dehydration.

Even colds and sore throats are caused dehydration, because when you're sick less desire to eat and drink. Fever dehydration increases.

4. professional athletes

Anyone can suffer from dehydration exercise, especially exercise in hot and humid climates or at high altitudes (eg tourism).

But professional athletes who train and compete in the marathon, high jump, climbing and cycling company, they are at greater risk of developing dehydration. This is because each time more exercise, maintain a body of water is harder.

During exercise, your body loses water, the more water that can be absorbed.

For every hour that you exercise, increases excretion of body fluids.

5. Those who live in the highlands.

Living, working and playing sports in the highlands (above 2500 meters) can cause a number of health problems.

One of the problems, dehydration usually occurs when the body tries to increase urination and rapid breathing, adapting itself to the heights.

Highlands faster breathing in enough oxygen in the blood to be maintained. No matter how you breathe faster, more water vapor to move out, the water body is less.

6. People who work outside the home and in the hot and humid or exercise.

When the weather is hot and humid, increases the risk of dehydration and heat exhaustion.

When the air is humid (moist), the sweat can not happen as fast as normal, the skin's surface to evaporate and cool you. This results in an increase in body temperature and body fluids is needed most.

Complications of dehydration

1. Thermal injury: If when you exercise so you sweat heavily, drink plenty of fluids, damage caused by the heat that you can muscle cramps and heat exhaustion or heatstroke fatal mild variable is.

2. cerebral edema, sometimes when after dehydration, water and fluid intake, your body will try to push more water into your cells. It makes some cells swell and rupture. This is especially dangerous when brain cells are affected and swelling.

3. Seizure: body salts such as potassium and sodium, the electrical signals from one cell to another brand. If your body's mineral balance, co-ordination, electrical signals are mixed together, resulting in the accumulation of involuntary muscles (seizures) and sometimes unconsciousness person.

4. The shock from loss of blood volume: This is one of the most dangerous and even deadly side effects are caused by dehydration.

When low blood volume due to dehydration caused a drop in blood pressure and oxygen levels in your body, the shock occurs.

5. Kidney failure fatal kidney failure problem occurs when your kidneys can no longer remove excess fluid and waste products from the blood and excrete.

6. coma and death if left untreated, severe dehydration prompt the body, can cause death.

Ways of dehydration

In most cases, a doctor will not see physical symptoms such as urine or decreased urination, depression and loss of elasticity of the skin (skin when we kill, to restoring the state will not be collected) detects water gives.

feet are cold.

The doctor may confirm the diagnosis and determine the severity of dehydration, you can write the following tests:

1. Blood tests to check the number of your blood sample is taken, for example, to check the amount of sodium and potassium salts in your body and how you make all of the work.

2. Urine test: Urine test can show whether your body is low and how severe it is.

If the cause is not apparent dehydration, doctors and other tests to check for diabetes, liver or kidney problems prescribes.

The evolution of terrestrial beings from amphibians which have evolved from water-living beings progressively decreased the water needs of these beings . The amount of water consumed directly or indirectly (through food, drinks etc.) is much less than the water used for other purposes. In water-scarce countries, drinking water sometimes becomes a luxury and people trek long distances to fetch a pot of water. 

Water intake changes from season to season particularly in tropical countries. Water consumption is high in hot summer months relative to cold winter season or humid rainy season months. Dehydration of children and the elderly is common during summer and they need special attention.

Dehydration in the human body occurs due to many reasons & among them are the types of foods one eats or the beverages one drinks. For example: Yogurt, fish, potato chips, and beans will cause thirst which is indicative of dehydration. Excess strong tea or coffee can cause dehydration directly or via more need for urination. Therefore, an adult is advised to drink about 2 liters of water per day & to eat more fruits (e.g. apples) to avoid thirst. Excessive water drinking can cause health problems so a balanced approach is better adopted. Anyhow, preventing dehydration in persons of all ages is one of the top health priorities & the Mayo Clinic (U.S.A) gives a good advice about that.

http://www.mayoclinic.org/diseases-conditions/dehydration/basics/prevention/con-20030056

I have a question to the expert. I´ve learned that marathon runners or triathlets can drink to much so the loose minerals and can collapse. Does someone have scientific informations to this problem? Thanks and regards

In routine, one can, being conscious, easily reverse mild to moderate dehydration by drinking more fluids -- but severe dehydration needs immediate medical advice/treatment.

The safest approach is preventing dehydration initially.

Keep an eye on how much fluid one lose during work, hot weather, sporting, illness or exercise, and drink enough liquids to replace the so lost water.

See link for unusual signs of Dehydration.

http://www.everydayhealth.com/news/unusual-signs-of-dehydration/

The question of dear Professor Hanno Krieger is great since knowing the reasons why a runner might collapse in or after a race could save a life, so it’s worth learning.

Possible causes of collapse:

1) Heat stroke is a potential cause since when one runs hard, the body generates a large amount of heat, and if it is not removed effectively, this will result in an abnormal high body temperature. This in turn causes massive, body-wide problems, which shows as confusion, dizziness, vomiting, and collapse. Dehydration can increase the risk of heat stroke, but it is not the only cause. Outside temperature and a rise of internal body temperature from hard work can also cause heat stroke.

2) Hyponatremia, a drop in the sodium that circulates in the blood, is another possible cause of collapse.

This occurs in a runner who drinks excess water during a race, which dilutes the sodium in the blood so much that it disrupts the body’s normal biochemistry. Hyponatremic runner also commonly vomits, becomes confused, and collapses.

3) Postural hypotension  is a relatively benign condition that happens in part because the runner has stopped running . During the high effort, at a race, the heart rate is very high, and as a result, so is the blood pressure. Also, the rapid, rhythmic contractions of the muscles upon running provide a strong pump-like effect on the blood vessels, encouraging blood to circulate back from the legs. On the finishing line, both of these mechanisms cease so the result is a sudden drop in blood pressure, which produces dizziness, fainting, and collapse, much like when one stands up too fast after sitting or lying down for a while.

Thanks dear Dr. Nizar Matar,

Hyponatremia were the accidents I heard of. But I was not sure because normally sodium, calcium and potassium concentrations are kept constant. Do you know the special biochemical process which interupts the normal regulation?

Dear Vilemar Magalhaes,

Need to drink two liters of water per day. Water is life. They say that you can live without food, can not live without water. I wish everyone a healthy life.

Be healthy, Shafagat

I´m no specialist for beer. But there is one point, beer without alcohole is still carrying calories. So from this point of view it´s not interchangable with pure or mineralic water.

Dear @ Roland, in the United States, beverages containing less than 0.5% alcohol by volume (ABV) were legally called non-alcoholic.  But UK uses these definitions:

No alcohol or alcohol-free: not more than 0.05% ABV

Dealcoholised: over 0.05% but less than 0.5% ABV

Low-alcohol: not more than 1.2% ABV.

So there is still some alcohol (empty Calories), but a lot less than normal beer with 4% alcohol, that's about 100 (empty) Calories for 12 oz.

When I was a student, we drank water after our hockey matches.  But now my students like isotonic drinks that still come with sugars and calories.

http://www.realbeer.com/edu/health/calories.php

One cannot single out one process for regulating or impairing the mass balance of sodium ions in the body. Several variables are at play & the interesting article, in the link below, throws some light on this intricate topic. 

http://cjasn.asnjournals.org/content/early/2014/08/05/CJN.12391213.full

Thanks for the paper, I´ll try to understand it.

Water is life, i think it is good to drink pure water to enable not only hydration of the body but also its internal cleaning; The better is to drink 1 to 1.5l per day. In hot and humid season,  people could loose more water and minerals by transpiration which could increase their need of  water.

Symptoms

In moderate dehydration, few or all the following symptoms can be present:

• Less frequent urination, burning urination, low amount of excreted urine;
• urine color may range from yellow to almost black (tea-colored). Urine is dark due to increased concentration of bilirubin.
• Thirst, possibly waking you up at night, but sometimes no thirst at all
• Dry mouth and lips
• Bad breath (halitosis)
• Poor appetite
• Dizziness and lightheadedness, balance problems
• Fatigue, drowsiness, sleepiness or insomnia
• Difficulty concentrating, impaired memory
• Nervousness (jitters)
• Moderate headache
• Stomach cramps (in food poisoning, gastroenteritis)
• Sensitivity to light and noise
• Anxiety, depression
• Nausea
• Constipation and associated bloating
• Thirst and waking up and drinking at night (polydipsia
• Jet lag
• Morning sickness in pregnant women

http://www.ehealthstar.com/dehydration/symptoms-and-signs

Dear Vilemar

The necessary amount will depend on three factors decided by the function of water in our body:

1. Maintain the system: For this purpose you have to drink what you have lost (by urination, sweating, etc.)

2. Maintain temperature: This is linked to the first. You have to drink more when when you sweat more (temperature is high, do more work)

3. Cleaning the system: Drink more if and when you have to remove more undesirable substances from your body.

Narayanan

Dear Narayanan,

your first two points are ok and understandable. But I have big problems with your cleaning function. All the time you can read "detoxify your body". But no one can tell me which poisons are excreted. I know the normal contents of urine and sweat. What shall be more?

Dear Hanno,

The list will be endless water soluble, here the question was about water.

And kidney has functions too.

Narayanan

Yes dear Narayanan,

but water shall be the carrier of substances. Show me a list. I think the best techniques will be to drink and eat the right things.

My problem is still. Do the concentrations of toxines change with the amount of water, or does the concentration on substances just  enlarge the concentration in urine. Thats what I have learned.

As per AYURVEDA, not only the quantity but a number of other aspects are also very important to keep our body properly hydrated as well to facilitate our systems to work smoothly e.g.:

1. Quality/Purity

2. Source / origin 

3  Situation 

4 Posture

5 Time of intake

7 Mode of intake

8. type of container .......

A little monograph can be prepared

Dear Vilemar,

I would suggest the exact number is dependent but the real number is the one that keeps us alive!

Douglas

In addition to water --- Fluid/water-containing drinks --  including fruit juices, soft drinks, tea, milk, coffee, dilute alcoholic drinks such as beer, etc. --- essential to maintain a human being properly hydrated.

Toxins in food nowadays are very real and there is almost no way to get around them. You can, however, still beat them. The best thing you can do for your body is to drink when you are thirsty and eat [minimally-processed food] when you are hungry. Even organic farmers use pesticides, so that just makes it important to wash your fruit. I don't think you need to take go as far as to dilute beer, but it is definitely a good idea to dilute stronger alcoholic drinks (and they usually taste better that way anyway).

I have read many things lately about toxins in the water so investing in a carbon filtration device for your drinking water would be great. This will filter heavy metals and organics out of your water, but (at least in the US) there is still a concern of the high fluoride concentration, mostly as SiF6(2-). Iodide is a good way to offset fluoride. It is found in iodized table salt, as well as some foods that you may eat on the regular anyway (like eggs and yogurt).

To offset the other toxins that you ingest, it is helpful to use spices like garlic, in particular, fairly liberally. Garlic is one of those superfoods that is good for your entire body, but I am specifically referring to it because it also helps keep your liver healthy. Many spices also contain essential oils that are [hepato]toxic if you severely overdo it, but you probably won't. Curcumin, found in tumeric, is particularly good at binding heavy metals like lead and mercury, so if you don't like curry, I suggest you acquire a taste for it.