National Aeronautics and

Space Administration

Educational Product

Educators Grades K–4

Educational Topic

Clean Water...Where Does It Come From?

Water Purification for the International Space Station

ET-1998-07-002-HQ Clean Water . . . Where Does It Come From? 

Objective

Students will construct a filter to demonstrate and simulate the water purification system on the International Space

Station.

Science Standards

Science as Inquiry

Life Science 

The characteristics of organisms

Organisms and their environment

Science and Technology

Understanding about science and

technology

Science in Personal and Social Perspectives

Personal health

Math Standards

Estimation

Measurement

Materials Needed 

(per group, class, or student)

Clear plastic soda bottle (2-liter)

Gravel (aquarium)

Sand

Aquarium charcoal (activated)

Cheesecloth (a nylon stocking can be

used instead)

Muddy water

Rubber bands

Food coloring (optional)

pH water testing kit (optional)

Vinegar (optional)

Background Information

The International Space Station inhabitants will join

the world in the effort of recycling. The recycling that

will be done is different than that which may take

place in your home or school. The astronauts will be

recycling their water. This includes respiration, perspiration, shower and shaving water, and even urine.

These waste waters will be purified and then used as

drinking water.

Biological treatments are used to purify water on

Earth. The microorganisms used in this process

destroy contaminants in the water. The International

Space Station will use physical and chemical

processes to remove contaminants. The Urine

Processor will remove volatile components in the

urine using distillation (heat disinfection used to prevent microbial growth). Less desirable and volatile

components will remain as a liquid brine, which will

be returned to Earth and disposed.

The International Space Station will also use filtration

and temperature sterilization to ensure the water is

safe to drink. Water will be checked often to ensure it

meets the water quality requirements and monitored

closely for bacteria, pollutants, and proper pH (a measure of the acidity or alkalinity in the solution). The pH

scale ranges from 0 to 14. Substances with a pH

value of 7 are neither acidic nor basic. Pure water has

a pH value of 7. The lower pH value indicates higher
Step 3: Stir the muddy water and pour it into the filter.

Watch closely as the water seeps down through the

three filtering layers of gravel, sand, and charcoal.

Discussion

1. What happened to the water while it passed

through the different layers of the filter?

2. Compare the muddy water to the filtered water. Is

there a difference?

3. Would it make a difference if one of the layers had

been left out?

Assessment

1. Have the students draw a diagram of the water filter.

2. Write a list of instructions for building a water filter.

Extensions

1. Collect and filter other samples of water containing suspended particles. A clay/water mix or

flour/water mix works well.

2. If possible, check the pH level of filtered water

samples and compare to unfiltered water samples.

3. Filter particle/water mixtures to which food coloring has been added.

4. Design and build a water filter using different

materials.

5. Write a description of how the water filter works

and the results obtained from the different

samples tested.

6. By checking the water clarity and the pH, determine how many gallons of muddy water can be

treated by the filter before the filter is expended.

For more information about the International Space

Station, please visit: http://station.nasa.gov

Please take a moment to evaluate this product at

http://ehb2.gsfc.nasa.gov/edcats/educational_topic

Your evaluation and suggestions are vital to continually

improving NASA educational materials. Thank you.

ET-1998-07-002-HQ Clean Water . . . Where Does It Come From? 

acidic levels; the higher the pH value the more alkaline the substance is. Public water systems have to

meet a pH level of 6.5 to 8.5. Even though the Space

Station water system specifications range from 6.0 to

8.5, the recycled water on the International Space

Station is almost sterile and much better than water

from a tap at home or at school. There is no odor or

bad taste. 

For Space Shuttle missions, it is not necessary to

recycle the water or waste products. The Shuttle fuel

cells produce water as a byproduct; however, water

recycling will be imperative for long-duration missions

such as on the Space Station or possible trips to

Mars. There will be no fuel cells on the Space Station;

therefore water will not be produced. In addition, a

spacecraft on a lengthy trip to Mars would be limited

to the amount of water it could carry because of

weight restrictions.

Water Filtration Model Activity

Note: This experiment only demonstrates a type of

water filtration. The experiment will not purify water

for drinking purposes.

Activity Procedure

Step 1: Cut the bottom off the soda bottle. Cover the

mouth with several layers of cheesecloth and secure

them with a rubber band. Suspend the bottle upside

down with its mouth over a glass to catch the filtered

water.

Step 2: Fill the bottle with charcoal to a depth of

5–8 cm. Place 8–10 cm of sand on top of the

charcoal. Place 5–8 cm of gravel on top of the sand.

Gravel

Sand

Charcoal

Cheesecloth