How do we remove unwanted substances from water? Watch this video to learn more about water purification.
Lesson E3: Water Purification
Figure E.1.3.1 – Astronauts live for months on the International Space Station.
Figure E.1.3.2 – Astronauts drink water from a purification system on the International Space Station (ISS).
Figure E.1.3.3 – The ISS recycles almost everything onboard, including water.
Reading
and Materials for This Lesson
Science in Action 8
Reading: Pages 344–346
Materials:
Large bowl, clear plastic wrap, salt, water, measuring cup, measuring spoons, masking tape, 1 or 2 small rocks (3 cm diameter), plastic cup (that fits inside large bowl), sunny location, tall plastic water bottle (1.5 L capacity), sharp scissors,
paper coffee filter, cotton balls (large handful), sand, rocks (2-4 cm diameter), water pitcher, dirt (containing tree needles and twigs), ruler.
Space Water Purification
The International Space Station is a spacecraft that circles around the Earth. Astronauts live on the International Space Station for months at a time. All of their food, air, and drinking water must be transported to the space station by rockets
from Earth. Due to limited storage room and the hassle of transporting water from Earth, engineers developed a water purification system on board the International Space Station. The system recycles astronaut urine into clean drinking water.
Watch More
Clean Water in Space
Watch this video to see Canadian astronaut Chris Hadfield demonstrate the International Space Station’s water purification system.
Connections
Figure E.1.3.4 – Wastewater treatment plants separate harmful substances from water.
Figure E.1.3.5 – Chlorine is added to clean water before sending it to homes.
Figure E.1.3.6 – Many stages of filtering are required during water treatment.
Connections – Health >> Water and Wastewater Treatment Plants
In towns and cities, homes usually don’t have personal water wells. Urban inhabitants get potable water from a central system. Fresh water in an urban water system originally comes from a river, lake, or well. Before this water travels through pipes
to people’s homes, it is cleaned in a water treatment plant. In a water treatment plant, large sediment particles are filtered out of the water. Chlorine is added to the water to kill any harmful microorganisms.
Used water from homes returns through sewage pipes to wastewater treatment plants. Here, water sits in huge tanks for several hours. During this time, sewage settles at the bottom of the tank and oily wastes float to the top. Both substances are removed
from the water. Instead of using chemicals, the water is disinfected with ultraviolet light before putting it back in the river.
Watch More
Safe Drinking Water
Watch these videos to learn more about the water treatment process.
Making sure water is safe to drink is an important job, because it can prevent thousands of people from getting sick. Watch this video to learn more about careers in water treatment.
Figure E.1.3.7 – Water faucets in campgrounds usually provide potable water.
Figure E.1.3.8 – Pump water filters clean water in the backcountry.
Clean Camping Water
People who go camping or hiking need a source of potable drinking water. Consuming water is especially important during physical activity, to prevent dehydration. Car-accessible campgrounds usually have a potable water tap or pump. However, backcountry
campgrounds usually don’t have a potable water source. Most people can’t carry all the water they need and it is not safe to drink water directly from a pond or stream. For example, animal feces with harmful bacteria like E. coli could be in
the water.
There are several ways to purify stream or pond water in the backcountry. Boiling water kills harmful bacteria and other microorganisms. One disadvantage to this method of water treatment is that the water takes time to cool. Another disadvantage
to boiling water is that it doesn’t remove any solids or dirty particles. Adding disinfectant tablets to water is a faster method of water treatment, but once again, it doesn’t remove larger sediments.
The best way to clean water in the backcountry is to use a portable water filter. These filters have very tiny holes that remove both large sediments and harmful microorganisms from water, making it safe to drink.
Figure E.1.3.9 – Chlorine tablets are sometimes used to purify wells and other water supplies.
Figure E.1.3.10 – Boiling water is effective in killing microorganisms, but leaves behind other substances.
Watch More
Water Filter Straws
Watch this video to learn about a simple portable water filter invention.
Watch this video to see an even better portable water filtration system.
Try It!
Make a Solar Still
Try this simple experiment to make a solar still that separates fresh water from salt water.
Materials:
Large bowl
Clear plastic wrap
Salt
Water
Measuring cup
Measuring spoons
Masking tape
1 or 2 small rocks (3 cm diameter)
Plastic cup (that fits inside large bowl)
Sunny location
Instructions:
In a measuring cup, add 2 tablespoons (60 ml) of salt to 2 cups of water. Stir well to dissolve the salt in the water.
Pour this saltwater mixture into the large bowl, to a height of approximately 3 cm.
Place the plastic cup in the center of the large bowl, right side up.
Cover the large bowl and plastic cup with clear plastic wrap. Tape the plastic wrap to the sides of the bowl, sealing the top of the bowl.
Place 1 or 2 small rocks on top of the plastic wrap, directly over the plastic cup. The plastic wrap should stretch downwards toward the cup, but not touch the cup. The plastic wrap should also not break.
Place the solar still in a sunny location, either outdoors or by a sunny window. Leave the solar still in the sunny location for several hours, or overnight.
Carefully remove the plastic wrap from the bowl and lift out the plastic cup without spilling. What do you observe?
Taste the water in the plastic cup. What do you observe? Taste the water in the bowl. What do you observe?
Watch this video to see a similar experiment and its results:
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Heat from the sun caused water to evaporate from the saltwater solution. The evaporated water cooled and condensed on the plastic wrap, trapping it inside the bowl. The rocks on top of the plastic wrap directed the condensed freshwater down
into the plastic cup.
This solar still was effective at separating salt from water, but it took a long time to separate a relatively small amount of water. It might be a good emergency solution on an ocean-travelling boat, but electricity-powered reverse osmosis
would be faster at distilling large amounts of fresh water.
Connections
Figure E.1.3.11 – Developing countries often lack potable water sources.
Figure E.1.3.12 – People need water to survive, but sometimes the water is too polluted to use.
Figure E.1.3.13 – Purifying unsafe water can save thousands of lives every year.
Connections – Technology >> Inventing Water Purification Solutions
People in developing countries often do not have access to water purification systems. Poor countries cannot pay for large drinking water and wastewater treatment plants, in both rural and urban areas.
Clean drinking water is a basic human need. Quick access to clean drinking water makes everyday life easier and prevents people from getting sick. Many humanitarian organizations are working to provide access to clean water for all people everywhere
in the world. Because there is no money to build and maintain large water treatment systems in some developing countries, environmental engineers are inventing small, inexpensive, and accessible water filters to purify water.
Watch More
Small-Scale Water Purification
This video explains how environmental engineers designed a small water purification solution in Bangladesh.
Try It!
Water Filter
Try this activity to build a simple water filter that removes sediments from dirty water.
Materials:
Tall plastic water bottle (1.5 L capacity)
Sharp scissors
Paper coffee filter
Cotton balls (large handful)
Sand
Small rocks (2-4 cm diameter)
Water
Water pitcher
Dirt (containing tree needles and twigs)
Ruler
Safety Warning
Take care with scissors; don't cut yourself or anyone else!
Instructions:
Cut the tall plastic water bottle in two, making the cut exactly halfway. You will now have a sort of jug and a funnel.
Turn the funnel section of the plastic bottle upside down.
Lay the paper coffee filter into the funnel. The coffee filter should be as wide open as possible, while covering the spout.
Completely fill the paper coffee filter with a 6 cm layer of cotton balls.
Pour a 4 cm layer of sand on top of the cotton balls. Some sand will spill into the cotton balls, which is okay.
Place a 4 cm layer of rocks on top of the sand.
Place the funnel section of the bottle into the jug, spout facing down.
Place a small amount of dirt, tree needles, and twigs into the water pitcher.
Fill the water pitcher halfway full with water, making muddy water.
Pour the muddy water over the rocks at the top of your water filter. Compare the muddy water in the pitcher to the water dripping out of the funnel. What do you observe?
Watch this video to see a similar version of this experiment:
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
The large rocks in the water filter removed the large particles first. As the dirty water travelled down through the filter, the sand, cotton balls, and coffee filter progressively removed smaller and smaller particles.
The water filter should have been pretty effective at cleaning dirty water. The water dripping out of the funnel might have been slightly yellow in colour, indicating that the filter could not remove some dissolved substances. However, the filter
should have removed any large dirt particles in the water.
You should not drink the water from this filter because the coffee filter paper does not have small enough holes to filter out harmful microorganisms. The filtered water should still be boiled or treated with a disinfectant before drinking it.
Sharing:
Congratulations on completing this activity! What does your water filter look like? Consider sharing your completed water filter in the course Sharing Forum.
Take a photo of it and post it; your teacher and other students would be interested in seeing how your water filter turned out!
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit E Lesson 3 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum,
or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
The process of distillation requires a lot of energy to boil and evaporate water. The fuel or electricity needed to heat large amounts of water is expensive compared to allowing sewage to settle at the bottom of a tank.
A good method to provide fresh water on the sailboat would be through a reverse osmosis system. The solar panels can provide electricity to provide pressure to force salt water through a reverse osmosis filter, separating salt from water. Distilling
salt water on the boat is less desirable because heating the water would require much more energy than the solar panels could provide. It would also take a long time to create fresh water from a solar still.
The chlorine in chlorinated pools has a strong smell, and its higher concentration irritates people’s skin and eyes. The small concentration of chlorine in a saltwater pool does not have a strong smell. Salt water does not irritate people’s
skin and eyes.
Locating wastewater treatment plants downstream from drinking water sources reduces the risk of accidental water contamination. Although sewage is removed before emptying wastewater back into the river, if any harmful substances accidentally
get back into the river, they won’t get into the drinking water supply and make thousands of people sick.
It requires a lot of energy to desalinate water, which is very expensive. Reverse osmosis desalination requires a lot of energy to force salt water through a filter. Distillation desalination requires a lot of heat to evaporate water. Fossil
fuels or electricity is needed for these systems, which is much more expensive than using the large freshwater supply that is already found on Canadian land.
Reading
and Materials for This Lesson
