Guiding Question:
Key concepts and vocabulary:
Storypath
Water Footprint
Water Footprint
Blue Water Footprint: The amount of surface water and groundwater required (evaporated or used directly) to produce an item.
Green Water Footprint: The amount of rainwater required (evaporated or used directly) to make an item.
Grey Water Footprint: The amount of freshwater required to dilute the wastewater generated in manufacturing, in order to maintain water quality , as determined by state and local standards.
What is a water footprint?
How else do you think our water footprint affects us all?
Dr. Arjen Y. Hoekstra 1967–2019
There is work to be done!
In 2019, Dr. Arjen Y. Hoekstra passed away from natural causes. He was very dedicated to his work. In his office there were papers left behind about some research he wanted to conduct around some goods that many people use without knowing how it can affect the Earth’s water supply. Someone needs to complete his unfinished work and there is news that you can take his place!
Working in groups or independently, you are now given the task to find the water footprint of four common goods used by us humans. The information you find may even surprise you, and that is ok!
Use the information to find the footprint of your class, grade, school or even your city! Record your findings on bar graphs to make it easier for others to see how decisions we make affect our water footprints and show your math skills!
Student Worksheets to Follow
What crop do you think is most commonly grown around the world? It’s sugar.
Sugar is found in a variety of foods that we consume–naturally occurring or as an additive. There are two main types of sugar that people grow: sugarcane (80%) and beet sugar (20%). You can find sugarcane usually in tropical and subtropical climates, and you can find beet sugar in mild climates in the Northern hemisphere.
Take a look at Map #1: Global Water Footprint for Sugar. What do you notice? What is interesting or surprising?
Sugarcane has a larger water footprint than beet sugar does. To make 2.2 pounds of sugarcane, you need about 470 gallons of water (one-tenth of a swimming pool). To make 2.2 pounds of beet sugar, you need 230 gallons of water. The countries that produce the most sugar are Brazil, India, Thailand, China, and the US.
Take a look at Map #2: Sugar Production in the US. What do you notice? What is interesting or surprising to you? Based on this map, what inferences can you make about the impact of sugar production in the US? Consider the source: The Sugar Association. What are the possible biases of the source?
In the US, people grew 34.6 million tons of sugarcane in 2022, and this represents an increase from the previous year. People in the US eat more sugar than people in any other country in the world. Usually, people in the US eat over 0.28 pounds of sugar each day, which is approximately half the weight of an iPhone or the weight of 1 banana.
Resources:
Sugarcane
“Water Footprint Assessment Tool” (originally from Mekonnen, M.M. and Hoekstra, A.Y. (2010))
Map #1: Global Water Footprint for Sugar
Map #2: Sugar Production in the US
When you hear the word “beef,” you probably think about hamburgers or steak, but you might not think about cows. Beef is the meat from cows that many people eat as a part of their regular diet.
Beef production makes up the largest part of the United States farming economy. In 2022, American ranches made $462 billion worth of beef. There are over 90 million cows in the US. US citizens eat 3 times more meat than the average person around the world. On top of having the world's largest cattle industry, the United States is also the world's largest user of beef—usually higher quality, grain-fed beef. An average American eats over 180 pounds of beef a year.
While many enjoy eating beef, they might not know that it has a huge water footprint. A water footprint is the amount of freshwater used to produce a good or service. There are 3 types of water footprints: blue water, green water, and grey water. Beef production has a large water footprint for blue, green, and grey water use. To make a single pound of beef, farmers and ranchers use, on average, 1,800 gallons of water. 98 percent of water use is from growing the food that feeds the cows.
While cows naturally graze on grass for their diet, most cows are primarily given corn or grain feed in the beef-production industry. Farmers and ranchers do this to make the cows grow up faster and fatter, but it wastes a huge amount of water and hurts the whole environment around the world. Just ONE cow can eat 1,000 pounds of feed in a few months.
As result of large water footprints like this, there is less and less safe and clean water for other purposes, like for drinking, cooking, and hygiene. By 2030, the amount of water needed could rise above the water available. The waste from cows and the fertilizer used to grow their food also pollutes the water not used to make beef.
If we want to help our global community and the environment, we need to figure out how to find more sustainable ways to produce beef and reduce our dependence on beef products.
Sources:
Foodprint. “The Water Footprint of Food.” FoodPrint, 8 Oct. 2018, https://foodprint.org/issues/the-water-footprint-of-food/.
US Department of Agriculture. “Cattle and Beef.” USDA ERS, 26 Sept. 2022, https://www.ers.usda.gov/topics/animal-products/cattle-beef/sector-at-a-glance/.
Beef
Healthy, Versatile Fruit
What food goes well in a taco, sushi, sandwich, or a salad? Avocado, of course! You can even add avocado to a smoothie or a brownie for a rich, healthy boost. Because they have a pit (or seed), avocados are a type of fruit. They are popular in many types of food from different cultures.
Avocados are known as a superfood because of their health benefits. Although they have a lot of fat, it is a healthy type of fat that is good for your heart. Vegetarians, vegans, and people who want to lower their cholesterol often choose to eat avocados because they are so filling and delicious. They also have many different types of vitamins, minerals, and fiber–all of which our bodies need!
Growing Avocados
Take a look at the graphs (Figure 1). What do you notice about how many avocados are produced each year? What do you notice about where they are grown?
Avocados grow in tropical or subtropical climates. Mexico is the country that grows and sells the most avocados, which are called “green gold” to show how special they are and how much money comes from selling them. The demand for avocado produces 40,000 to 60,000 jobs but also puts communities in severe drought for months at a time.
When they are eaten, avocados do not contain a lot of water, but they have a large water footprint because they require a lot of water to grow. It takes a bit less than 75 gallons (about 280 liters) of “blue” water* to grow a pound of avocados. This is more than 10 times the amount of water needed to grow tomatoes, another popular fruit. In the U.S., each person eats an average of 8-9 pounds of avocado per year.
Growing avocados can have a negative impact on people and the environment. Because avocados are so important to the economy, farmers often cut down other types of trees to make more space for growing avocados. This can be bad for the soil, and it also doesn’t leave a lot of space to grow other types of crops. As a result, people who live around avocado fields often do not have access to enough food to eat. Additionally, since so much water is needed for the avocados, local communities may not have access to the water they need to survive.
As demand for avocados continues to climb, it is important to find more sustainable, fair ways of growing this nutritious fruit.
Note: Blue water comes from rivers, lakes, streams and aquifers; it
does not include rainfall (“green” water) or recycled (“grey”) water.
Sources:
Avocado
Figure 1. Development of global avocado production (upper panel) and for the six most important producers (lower panel) between 1961 and 2018.
Source: FAOSTAT
https://www.freshfruitportal.com/news/2022/01/06/avocado-production-water-footprint-and-socio-economic-implications/
Winters bring dry weather to Mexico City, with averages of just one day and one-fifth of an inch (5 millimetres) of rain a month. During summer, the monthly rainfall averages out to 12 days and a total of 2.4 inches (62 mm) a month.
Avocado
“It Never Rains in Southern California”
That is over 5,200 reflection pools of water!
Part of this is because it takes a lot of water to grow cotton and turn it into a t-shirt. Part of it is also because of how many t-shirts are made each year. One pound of cotton requires 1,320 gallons of water to grow. One tshirt needs 8 ounces of cotton. We also make 2 billion t-shirts every year. Cotton is the crop that uses more water than any other crop in the agricultural industry.
What happens when we use water to make cotton? Well, the countries that produce the most cotton, such as India, Pakistan, China, the United States, and Turkey are all running out of water. When water is scarce, it’s harder to grow food and people get sick. The UN says that 80% of diseases in developing countries come from lack of access to clean water and sanitation.
For example, the Aral Sea in Central Asia used to be the 4th largest lake in the world. The Cotton Factories on the shores of the Aral Sea used so much of its water that it shrunk to less than half of its original size.
Not only is the amount of freshwater shrinking, but the water is also being polluted because of cotton production. Fertilizer and pesticides from cotton fields end up flowing into nearby water sources, harming the health of the plants, animals, and human beings living nearby.
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Cotton comes from a plant called Gossypium. The Gossypium plants have soft, fluffy, hair that protects their seeds. This is the cotton. Cotton is turned into fibres which we use to make fabrics.
Cotton fabric can be used for things like couches, curtains, and also clothes. The fashion industry is the largest user of water. In one year, the fashion industry used 20,869.6 gallons of water.
Cotton
Sugarcane
What is it? What is it used for?
Water Footprint. Should include specific data
Beef
What is it? What is it used for?
Water Footprint. Should include specific data
Avocado
What is it? What is it used for?
Water Footprint. Should include specific data
Cotton
What is it? What is it used for?
Water Footprint. Should include specific data
Data Gathering
| Gallons of water to grow/produce 1 lb |
Sugarcane | |
Beef | |
Avocado | |
Cotton | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
Sugarcane | Beef | Avocado | Cotton |
Name of product
Gallons of water needed to grow 1 lb of product
2,000
1,750
1,500
1,250
1,000
750
500
250
0
Data Gathering
| # of classmates who eat/use that product weekly (use tally marks) | Gallons of water to grow 1 lb of product | Total amount of gallons of water used |
Sugarcane | | | |
Beef | | | |
Avocado | | | |
Cotton | | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
Sugarcane | Beef | Avocado | Cotton |
Name of product
Gallons of water needed to grow 1 lb of product
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
0
What can be done?
I do
What small changes can you make in your life to help with your issue?
We do
What can our community do to make a difference with this issue?
They Do
What can people in positions of power do? Can we do anything to advocate for them to take these actions?