Activity # 2
My Water is Gray Water
Grade Level: 5-8
Students will determine the average amount of water they use during a typical
shower and the concentration of soap in that water. The students learn the
need to recycle gray water to allow plants and animals (including humans)
to survive in space.
- How much water do we use in a typical shower?
- What is in my gray water?
- What is the concentration of soap in my gray water?
- Besides soap, what else might show up in gray water?
- Do longer showers use more water?
For the class:
For each student:
- Stopwatch or timing device
- Balance (ideally, triple beam)--metric
- Access to showers
- 1 bar of unused soap (can be brought in by students; if so, have
a few extra bars on hand for those who forget)
- "My Water is Gray" student worksheet (two pages;
masters on the following two pages)
- Empty 2 liter bottle
Photocopy a "My Water is Gray"worksheet (two pages) for each student.
Gather all of the necessary materials. If you choose to have students
bring in bars of soap, assign this before the day of the activity.
If your school has no showers for students to use, then this activity
can be adapted with the "take 3 showers" part as a homework assignment.
Name: _______________________________________ Date: _________
My Water is Gray Worksheet
Determine average shower time:
Length of shower
Shower 1:________min________sec = ____________sec
Shower 2:________min________sec = ____________sec
Shower 3:________min________sec = ____________sec
Total time for three showers = ____________ sec
Average shower time = total time for all three showers (in sec) ÷
Average shower time = _____________sec
Average shower time = ________min ________ sec
Determining Average Amount of Soap Used Per Shower
Weight of unused soap ___________ g
Weight of soap after 3 showers ____________g
Weight of unused soap minus weight of soap after 3 showers = Amount of soap
Total amount of soap used for three showers = ______________ g
Average amount of soap used per shower = total amount used for three showers
Average amount of soap used per shower = ______________ g
Determining Flow Rate of Shower
1. Turn shower on completely; place bucket under shower head, and time for
2. Measure volume of water in bucket after one minute by pouring into two
liter bottles. Round to the nearest quarter liter.
Flow Rate of Shower = _____________ liters per minute
Determining the Amount of Water Used During an Average Shower
Average amount of water used per shower = average shower time x flow rate
Average amount of water used = ________min x _______ liters/minute =
Determining Concentration of Soap in a Typical Shower
Soap concentration = amount of soap (in grams) ÷ volume of H2O (liters)
= ___________ grams per liter
Determining the Cost of a shower in Space
Use the following information to determine how much your shower would cost
(this is a one time use of water -- not yet recycled).
1 liter water =1 kg
1 kg = 2.2 LB
Cost of sending 1 LB into space = $10,000
___________ = Cost of Shower
1. Discuss with the class the importance of using water efficiently in space.
Ask the students what might be different about how we would use water in
2. Hand out a “My Water is Gray” student worksheet to each student.
3. Have the students weigh their unused bars of soap (in grams or convert)
and record this measurement on the student worksheets.
4. Tell the students to go take three showers, using their bars of soap
and timing how long each of the three showers lasts. Time starts as water
is turned on and stops when water is turned off. (This step and the next
one can be homework if necessary.)< p> 5. To measure the flow rate of
the shower the students must measure the volume of water flowing in one
minute. This can be done by putting a bucket under the spout and collecting
water (with valve set a “normal” shower position) for one minute (60 seconds
). They can then measure the amount of water collected by seeing how many
2 liter bottles-full of water were collected.
6. Back in class, ask students to weigh their bars of soap again. Have
them determine the average amount of soap used per shower by dividing
the mass of soap used by three (record on student worksheet). They can
also determine and record on their workshe ets:
a. the average amount of time per shower by dividing the total
shower time by three.
7. Students will now know the amount of soap in one of their typical showers
as well as the amount of water used. They can now determine and record on
their worksheets the concentration of soap in their gray water (expressed
in grams of soap per liter of water).
b. the amount of water used in a typical shower by multiplying the flow
rate by the average time for a shower.
8. Students can determine how much their shower would cost in space
using the following information:
1 liter water =1 kg 1 kg = 2.2 LB Cost of sending 1 LB into
space = $10,000
1. Ask the students what they feel they learned in this activity. Were they
surprised by any of their results? Have your students recall the discussion
they had at the beginning of this activity and ask them if they have any
new ideas about the importance of using water efficiently in space? In light
of the high cost of bringing water into space, ask students how their findings
might relate to the challenge of growing plants in space.
2. Students can generate a list of all other substances that might appear
in their waste water (shampoo, toothpaste, perfume, hair spray, etc.).
Which of these might appear in an astronaut's gray water (hair spray,
lipstick, cologne, etc. probably would n ot). Use the worksheet "What
is in your Gray Water" or you make wish to make a transparency of this
3. Students can graph their results (Show sample "Bar Graph")
4. Discussion of averages and statistics
- Soap concentrations used in the activity
- Length of showers- boys vs. girls
- Number of showers per bar of soap
- Frequency of favorite brands brought to class by students
- Why include measurements from three showers?
- Why add the individual shower times and divide by three?
- Is the average concentration a better measurement than would be calculated
precisely for an individual shower? Discuss the precision of measurements
versus the adequacy of measurements, i.e., what is "good" data?
Background for Teachers
Gray water is used water (water containing soaps, waste and other contaminants).
In space, scientists hope to use gray water to grow plants. The major contaminant
of water in space will be the soap that the astronauts use to cleanse themselves.
A nutrient solution can be mixed with this gray water and then this solution
can be fed to the plants. Plants take up water through their roots, use
it for different chemical reactions (like photosynthesis) and then transpire
it through their leaves. Transpiration occurs when water evaporates through
tiny holes in the leaves. This transpired water is pure regardless of how
pure or "gray" the nutrient water was. The plant itself provides the filtration
- Graph 2-D data in various forms
- Convert minutes to seconds, ounces to grams
- Gray water - water that has been used and has contaminants
- Contamination - introduction of an undesirable or harmful material
- Concentration - the amount (by weight) of a stated volume
- Flow rate - the volume of fluid passing a given point per unit period
- Transpiration - release of water vapor through pores or membrane
- Calculating quantity of water and soap used in a typical shower
- Calculating the concentration of soap in their gray water
- The importance of using gray water in space
- Plants can help in recycling gray water
More Activity Ideas
See the Internet site for NASA Project STELLAR at
http://stellar.arc.nasa.gov for the following related activities:
Activity #12 on Toxic Bio Assay Demonstration
Activity #13 on Toxic Bio Assay Laboratory
Keywords: Hydroponics, Gray Water, Transpiration