QUESTIONS III
1. The Earth’s hydrologic or water cycle consists of several reservoirs for H2O connected by flows of water
or water vapor. The typical textbook representation of the hydrologic cycle usually is a cross-section
diagram of a small part of Earth’s surface with an ocean, landmass, and clouds. A box model (Figure III.1)
is another representation of the cycle that emphasizes the connections (arrows) and the importance of both
groundwater and the cryosphere (ice). List and identify by name the different symbols in Figure III.1. One,
the letter P, is provided as an example below.
P—Precipitation
2. Determine how many gallons of water you use in a day. Consider a rainy and cold Saturday, when you
spend most of the day in your house or dormitory. To determine this amount, go to the USGS website that
has a calculator for determining water usage on a per-capita basis: http://ga.water.usgs.gov/edu/sq3.html.
Record your answers in Table III.1 below and be ready to explain in class why your “Saturday per-capita
value” is higher or lower than the average of the class.
Students will fill in the table based on their personal water use. The calculator uses the following factors
3. List any other water uses or factors that might increase or decrease the amount of water used in a
single-family home.
Uses not in the calculation include lawn watering, gardens, car washing, etc. Also the habits of
toilets. Older toilets and appliances use more water than new, low-flow models.
4. According to SIWI–IWMI (2004), between 300 and 3,000 liters of water are needed to produce a
kilogram of grain. Each one of us, depending on our diet, is responsible for the 2,000–5,000 liters of water
used to produce the food we consume each day. This water is “hidden;” it does not show up in our
household water calculations. If we are seeking to understand water use in a region, this agricultural use
must be taken into consideration.
a. Given that 1 gallon (U.S.) of water equals 3.78 liters and assuming the food in your daily diet required
4,000 liters of water to produce, how many “food gallons” of water per day are you using?
b. How many times greater is the quantity of “food gallons” than the value of your standard household
gallons calculated in Question 2 (above)?
5. Table III.2 provides average water requirements for production of food items. Use it in answering this
question.
In Table III.2, the water requirement given for cereals is up to 3 m3 per kilogram. Below, in a conversion
example, this quantity 3 m3 / kg is converted to gallons (U.S.) per pound.
a. From data in Table III.2 and the example above, how many gallons of water are used to produce a pound
of grain-fed beef? (Hint: Simply consider how many times greater is the use of water for beef than the upper
limit of water for cereal.)
b. Complete column 2 in Table III.2 with the equivalent number of gallons per pound.
Poultry = 6 x 120, or 720 gallons per pound
c. Estimate your weekly intake of selected foods in pounds or kilograms and record in Table III.2.
d. Determine your weekly “food gallons” or “food liters” of water per week and record in column 4.
Students determine individual answers by summing their weekly gallons. For some college students, it
6. As human population increases and changes in diet (more protein) continue, more food will be needed. At
the same time, groundwater depletion due to irrigation threatens the needed increase in food production.
What options would you suggest for addressing this problem?