A typical Human is about 70% water [some Intro Biology texts quote up to 80%]. In part, the high
water content of Humans is intracellular; cytoplasm [literally plasm means “stuff” and the
prefix cyto- refers to cells, so cytoplasm is “cell stuff;” protoplasm substitutes the
prefix proto- (or first) for the cyto-, so protoplasm is “first stuff” and describes the
cell contents]. Protoplasm is a suspension of proteins (and miscellaneous other stuff) in water,
along with numerous dissolved substances in the water. Virtually all metabolism takes place in
aqeous (water) solution. Just outside the cell membrane in most tissues, is a water-filled space,
called interstitial space, which is a complex solution of substances needed to support metabolism,
and of by-products of metabolism. Beyond the interstitial fluid is the serum, which closely resembles
the interstitial fluid plus the formed elements of blood. The heart pumps the fluid (water) and
everything else is transported in the current. Frequently, the abundance of water in living organisms
is used to justify declaring water to be an important nutrient [this is done in all Nutrition texts
I have read recently, most Health references and many introductory Biology texts]. But, is it really
Water is lost from the Human body (1) as the solvent in excretion of wastes by the kidneys, (2) during the cooling side of thermoregulation (sweat), (3) as humidity in exhaled air, (4) in fecal material (the softer the stool, the higher the water content), and (5) is chemically ‘consumed’ in hydrolysis or catabolic reactions (but is ‘produced’ in dehydration or anabolic reactions). If you have ever been involved in I & O charting on patients [if you haven't yet, just wait… it's one of the many ‘fun’ things Nursing students get to do], you know that the expectation is that the output is matched by the intake. So, intake of water is necessary, usually quoted as 9 to 12 cups [2.2 to 3.0 liters, or 1 to 1½ two liter bottles] per day. For a while, many ‘authorities’ were saying that the water intake had to be water, not coffee or other beverages. Then during 2007, these authorities finally realized that coffee actually does contain water [when Nescafé® Taster's Choice 100% Columbian is made according to directions on the jar, the resulting instant coffee is 99.2% water by weight]. Caffeine is a diuretic, so the 6 oz cup of coffee which is 185 ml water and 2 g coffee may not supply 185 ml water, but will provide more than 2/3 cup (165 ml) water [so you would only have to drink 1 to 2 pots of coffee a day to meet your “required” intake; the same argument applies to other caffeinated beverages such as brown soda pop]. I would not expect any reasonable Human to calculate the water content, much less effective water content, of beverages (or foods [see illustration 25.2 in your text (pg. 25-3) for examples of the water content of foods]), but some of you OCD-types might consider it. Some non-authorities promoted bottled water as a means of ‘flushing’ toxins from your body, but the kidneys don't work that way. Drink more than enough bottled water one day, and you will end up producing more dilute urine -not more urine volume of equal concentration to days when your water intake roughly matched output. Grams of toxins excreted is independent of volume of water excreted, except during episodes of sub-clinical dehydration.
How much water do you actually need? The best advice to give concerning water intake is, “If you're thirsty, drink; when you're no longer thirsty, stop drinking.” However, beverages containing alcohol don't count. Alcohol is dehydrating, even at the relatively low concentration found in “lite” beers (roughly 3.2 - 4 % alcohol). An 8 oz can of 3.2% alcohol beer does not provide any water although it contains about 7.7 oz water. Any higher alcohol content beverage definitely yields negative net water intake due to dramatically increased output. Real water has zero calories, yet some bottled (flavored) water has more than 200 Calories per bottle [one even advertises that their bottle water is ‘better’ because it has “only” 95 Calories, while the ‘best’ water contains zero calories]. These bottles of “water” get their Calories from added sugars, probably corn syrup. Any sugared beverage will stimulate thirst, so the part about “when you're no longer thirsty…” doesn't happen until after you stop drinking, and your blood glucose recovers back down to normal.
The other way to monitor your water intake is the color of your urine. Normal urine is pale straw yellow. As the patient becomes progressively more dehydrated (sub-clinical), the urine becomes progressively brighter yellow; excess water intake causes the urine to become lighter (or even clear).
Water deficiency, or clinical dehydration leads to a
nauseated feeling, rapid heart rate, increased body temperature, dizziness, difficulty in moving,
kidney failure and death. Up to the onset of difficulty in moving, this condition is fully reversable
without long term complications by ingesting fluids. Even after the onset of difficulty moving, the
administration of IV fluids is usually sufficient for quick recovery.
Water toxicity or Hyponatremia (low blood sodium due to water overdose) leads to water accumulation in the brain and lungs, confusion, severe headache, nausea, vomiting, lethargy, seizure, coma and death. Water intoxication may be uncommon, but it is not rare. It can occur in any situation where the patient is sweating a lot (for example, outdoor work or athletic competition on a hot, humid summer afternoon), drinking lots of water, but not replacing electrolytes lost via sweat. Up to and including lethargy, this condition can be reversed [but not as quickly as for dehydration] by ingesting salty foods or even salt tablets, while applying cool compresses to lower skin temperature (and reduce sweating). Beyond this point, the administration of IV isotonic saline is necessary.
[disclaimer: Treatment descriptions for water deficiency and water toxicity are based on first aid training, and should not be taken as recommended Nursing interventions.]
In those states where I have some familiarity with the regulations, municipal water supplies are
subject to mandatory testing at least once a day [most major municipal water supply facilities do
hourly inspections, based on conversations with management level employees]. Reporting requirements
are weekly, except “immediately” on certain defined events; and the state Health Department
has staff who read these reports, and alert their supervisors of situations requiring a “boil
until cancelled” notice to be issued. Commercial water bottlers are allowed to inspect their
water whenever they feel like doing so. Their findings can be released to whomever the company wishes
as often as the company cares to do so; and the state Health Department has limited staff whose
responsibility is to file the unread commercial bottlers' reports in the appropriate file cabinet.
So is bottled water safe? There are no guarantees, but the reputation of the company, and consequently marketability of their product, depends on the absence of rumors of problems with their water. On the other hand, it is unclear how buying bottled water (typically $1.35 to $3.45 for 12 oz [$14.40 to $36.80 per gallon], or $3.64 to $9.31 per liter) compared to municipal tap water (“free”) [one town in North Carolina charges about $0.37 per gallon, or $0.10 per liter for water] can be considered to make economic sense. The bottles are convenient for transporting water, but can be refilled with tap water several times before cleaning (or discarding, maybe even recycling them [to make polyester fabric]). If you have well water in northwestern Indiana [the Kankakee River basin] refilling these bottles at home may not be a good idea [the ground water has several hundred percent of EPA allowable iron and sulfur for drinking water]. On the other, other hand, buying bottled water does “stimulate the Economy.”
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revised: 12 Nov 2009