At this time, some of our sons and daughters are involved in the military operation in Iraq.  I watched the television set this morning showing water gushing from the water main in Bagdad with the statement that the water is not available to the entire city at this point.  We are getting letters home describing temperatures between 130 and 150° F, values that I didn’t even know existed on this earth.  I certainly didn’t expect to people to be living where there would be temperatures like that and at the same time have a water main break.

     Water is by far the major component in the human body making up 60% of normal body weight.  If a person weighs 150 lbs, they have 90 lbs of water their body.  Our kidneys are very finely tuned to measuring how much water we take in, how much water we put out and then urinating out the right amount each day.  But in order to get rid of the waste products that the body generates each day, there has to be at least a pint of urine per day or the person gets into kidney failure.  If the person quickly looses 5% of their body weight as water lose, usually, they are in significant compromise.  If they lose 10% of their normal body weight to dehydration, the person is critically ill.  A 15% loss of body weight is frequently fatal.

     Myths and impressions about water and its importance to the body abound.  To use a word that I have described before, our bodies are equipped to maintain homeostasis.  “Homeo-” is part of a word meaning body; “-stasis” means staying the same.  Thus our bodies are equipped with a system that keeps our body composition the same day to day to day to day.  When you get up in the morning, your weight is generally pretty much the same that it was the day before.  Your salt concentration in your body will be the same, your potassium will be the same, the calcium will be the same, etc. etc.  These are all balances that are maintained involuntarily by hormones, sensory organs and the kidneys.  The kidneys add up how much sweat a person has, how much salvia they make, how much urine they make, how much water is lost in the stool during a day.  They even know whether the person has been vomiting.  This inventory system is then attached to a thirst mechanism that tells the person to drink fluid in an amount equal to whatever is lost.

     In the past many years in the United States, water and many other liquid drinks are consumed not because we are thirsty but because we have social habits.  People do not drink coffee or Coca-Cola because they are thirsty. The amount of Coca-Cola consumed is not done to quench thirst so much as it is to satisfy other needs.  In normal human society, the need to drink a glass of water to satisfy fluid intake is relatively unusual.  Our fluid intake needs are usually met by the social practice of drinking coffee, coca-cola, milk, beer, wine, juice, etc as part of meals or friendly get-togethers.  These socially mediated fluid intakes usually exceed the bodie’s absolute fluid requirements.  Thus, the body’s problem becomes what to do with all the extra water that is taken.  Clearly one of the most magnificent complex organs in the body is the kidney.  It receives many messages from all over the body each day and somehow is able to figure out how much water a person has taken in and it knows how much water to put out.
     To review some statistics regarding how much water a person needs each day, we know that the body looses about  one quart of fluid each day to perspiration and breathing.  There needs to be at least one pint of urine produced per day and so the body needs at least 1 ½ quarts of water each day to maintain balance.  That is a minimum number.  A more ideal number would be about 2 quirts fluid intake per day.  Obviously, in today’s heat  a person doing physical labor may sweat two quarts or more and that loss may take much more than two quarts per day.

     I hear from many patient’s that they think that they should drink a large amount of water to “flush their kidneys”.  This is an invalid concept.  Every day the kidneys filter 120 to 150 quarts of blood.  This cleaning, filtering process that the kidneys carry out does not depend on how much water the person drinks.  Drinking more water does not lead to cleaner kidneys.

     There is one situation in which drinking more fluid is beneficial and that is to a person who has kidney stones.  In order to dilute out the waste products from the kidneys so that stones do not occur, these individuals should produce approximately 3 quarts of urine per day and they need to take in approximately 4 quarts of fluid per day to avoid kidney stones.  This is hard to do in a day and day basis and these people get tired of urinating so much.

     The problem of too much water is most evident in people who have a heart weakness.  Normally, the heart pumps about 5 quarts of blood per minute.  In ancient times when hearts sometimes pumped less blood, it was because the person was dehydrated.  In those days, nobody lived long enough to get heart disease.  In ancient times when a person became dehydrated, those who could best conserve water did so by developing a message service from the heart to the kidneys.  The heart would know that it was not pumping enough blood and would send a message to the kidney saying please save salt and save water because the body is running out .  The kidneys would respond by doing that and the person’s life would be saved  in times of water deprivation. However, in this modern time of 2003, such is rarely the case.  We have lots of water.  Now when a person’s heart is not pumping enough blood, it is because the heart is diseased.  However, the message that the heart sends to the kidney is exactly the same.  The heart still believes that the body is dehydrated when it is pumping less blood than usual.  When this occurs, the kidneys get a message to save water.  As a person continues to drink they accumulate fluid and get something called edema in which the ankles swell.  In grandmother’s time, this was called dropsy.  In this situation, water actually becomes poisonous.  More water can build up in the ankles and eventually into the lungs and the person becomes very short of breath because there is no room to get air in the lungs.

     The message from this column would be that a normal person usually does not have to think about how much fluid they are drinking.  They drink whatever they will and kidneys do their job of adding how much came in and how much needs to go out.  The next morning the person weighs just the same amount that they did the day before.  Note that a pint of water weighs 1 pound.  Day to day the kidneys may be off one pound or two pounds but rarely more than that.  However, when a person develops heart problems, then the amount of water that is excreted each day may be less than is taken in and swelling of the ankles and perhaps swelling into the lungs may become a major problem.  Thus the idea that a person has to “drink eight glasses of water per day” becomes a very harmful practice.  Sometimes we have to use water pills to get rid of the excess water that a person with heart problems may hold onto.  This is always made easier if the person does not drink excessively.

     A last and interesting question to be, “What is the most urine the kidneys can put out in a day?”  For a normal person this is around 20 quarts of urine a day.  Thus if a person just had to, they could drink about 20 quarts of fluid a day and still maintain balance.  This is not a recommended habit to get in to.