Water Content of Body and Food, How Much Water Should You Drink, Percents, Simplify Fractions

Up to 60% of the human adult body is water. The brain and heart are composed of 73% water, and the lungs are about 83% water. The skin contains 64% water, muscles and kidneys are 79%, and even the bones are watery: 31%. The weight of water is 8.33 pounds per gallon, so if you estimate it at 8 pounds, it is easy to calculate how many gallons of water is contained in your body.

If Mr. Kramer weighs 160 pounds, we can take 60% of that number. The easiest way to do that is to break up 160 into tenths, so each 10% is 16. Since there are six 10%s in 60%, we multiply 16 by 6 to get 96 pounds of water. Then we need to divide 96 pounds by 8, the weight in pounds of a gallon of water, to get 12 gallons. I had two 5 gallon buckets and two 1 gallon buckets in class and the children could physically see how many buckets I would fill if I were rung out.

Water serves a number of essential functions to keep us all going:

1. A vital nutrient to the life of every cell, acts first as a building material.
2. It regulates our internal body temperature by sweating and respiration.
3. Carbohydrates and proteins that our bodies use as food are metabolized and transported by water in the bloodstream.
4. It assists in flushing waste mainly through urination.
5. Acts as a shock absorber for brain, spinal cord, and fetus.
6. Forms saliva.
7. Lubricates joints
8. The only natural substance that is found in all three physical states—liquid (water), solid (ice), and gas (fog/clouds)—at the temperatures normally found on Earth.
9. Freezes at 32° Fahrenheit (F) and boils at 212°F at sea level.
10. 1 gallon=4 quarts=8 pints= 16 cups and 1 cup=8 ounces; 1 gal=128oz.
11. Pure water’s chemical formula is H₂O which means that each molecule contains two hydrogen atoms and one oxygen atom connected by covalent bonds.

In order to replenish all the water we lose in a day through sweat, respiration, urination and other waste, we need to consume 80-100 ounces of water per day, not including water in your food (the old standard of 64 ounces of water was not based on any sound evidence).

The Institute of Medicine’s daily general fluid intake recommendations:

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  • 91 ounces (that's 11-plus 8 ounce cups a day) for women 
  • 125 ounces (15-plus 8 ounce cups a day) for men
  • Drink 1 cup of water 30 minutes before each meal

Remember, these guidelines are for total fluid intake, including fluid from all food and beverages. Approximately 80% of our water intake comes from drinking water and other beverages, and the other 20% comes from food. Assuming these percentages are accurate for most of us, the recommended amount of beverages, including water, would be approximately:

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  • 9 cups for women or 72 ounces of water per day
  • 12.5 cups for men or 100 ounces of water per day
  • drink even more water if it is hot, humid, and/or if you are very active 

While 20% may seem like a lot of fluid to get from food, many common food items are mostly water (see below). I asked the children to indicate which of these high water content foods they eat on a regular basis and asked them to track their consumption during the week. 

I also challenged the children to record the amount of water they drink in 8 ounce increments. Circle each multiple of 8 to tally your water intake during the day; and for grades 2-6, add your weekly total and divide by 7 to find the daily average.

[For example, if your water bottle is 16 ounces, circle two multiples of 8 for each bottle you drink; if your water bottle is 24 ounces, circle three multiples of 8].

I thought this was a great opportunity to look at more foods and other non-food materials and their water content percentages. I had the children shade these percentages in on a horizontal bar broken up into 10 sections. It was amazing to watch children from K-6th grade be able to shade in percentages to acute accuracy. I had the older children from 3-6th grade look at each percentage as a fraction and then simplify that fraction.

When representing any percentage as a fraction, simply divide the percentage by 100 (so 50% is 50/100; 85% is 85/100). Now for the fun part, when the fraction is 23/100, it is already simplified because 23 and 100 do not have any common factors other than 1 (23 is prime so none of the factors of 100 [2, 4, 5, 10, 20 …] can be divided evenly into 23). However, if the fraction is 50/100 you can see that 50 is the largest common factor of both 50 and 100 so 50/50=1 and 100/50=2 so 50/100=1/2. Simplifying 85/100 is a little more difficult since 5 is the only common factor (85/5 is 17 and 100/5 is 20 so 85/100=17/20; another observation is the since 100/5=20 you can see that 85 is 3 less 5s than 100, so 20-3=17). Simplifying 84/100 is fun because you can cut each number in half twice: 84/100=42/50=21/25.

Drink water!!