Week 19 · Theme 3 Protecting Our Planet, Unit 3 Our Earth’s Resources, Concept 3.2 Water as a Valuable Natural Resource (B) · 3 lessons
1
Fresh water, frozen and hidden
Discovery Education Science P5: Term 2, Unit 3, pp. 41–43
GoalShow how Earth’s fresh water is divided between ice, groundwater and easy-to-reach water, and explain why fresh water is scarce.
New words
scarcity · when there is not enough of something that people needglacier · a huge, slow river of ice on landdrought · a long time with very little rain
Explanation
Only about 3 out of every 100 parts of Earth’s water are fresh, and most of that is hard to reach. About 70 out of every 100 parts of the fresh water are frozen in glaciers and ice caps. About 29 parts lie underground as groundwater. Only about 1 part in 100 is easy to reach, in rivers, lakes, ponds, soil and the air. People, land animals and plants can use fresh water but cannot drink salt water, so fresh water is a precious resource. In many places there is scarcity, which means there is not enough, often because of drought or pollution. People build dams to store water and canals to carry it, but many people in the world still do not have safe water. These numbers are rounded, to show the pattern.
Worked examples
Imagine 100 squares for all of Earth’s fresh water. About 70 are ice, about 29 are underground, and only about 1 is in rivers, lakes and the air.
Part of fresh water
Out of 1000 mL
ice
700 mL
groundwater
290 mL
easy to reach
10 mL
If a 1000 mL bottle stood for all fresh water, the parts would be 70 × 10 = 700 mL for ice, 29 × 10 = 290 mL for groundwater and 1 × 10 = 10 mL for easy-to-reach water. 10 mL is only two teaspoons.
Water
How easy to reach?
river or lake
easy
groundwater
needs a well
glacier
very hard
Some water is easy to use and some is hard. A river is easy to reach. Groundwater needs a well. Glacier ice is far away and frozen.
Class activity
Hidden water model (a grown-up helps). Fill a clear cup with dry sand to the top. Slowly pour 100 mL of water onto the sand and watch the water disappear between the grains. Dig a little hole and see the water collect. This shows how groundwater hides in the spaces between grains of rock and sand. Do not drink the water.
Practice
1
Where is most of Earth’s fresh water?
Frozen in glaciers and ice caps.
2
If 1000 mL stands for all fresh water and about 70 out of every 100 parts are frozen, how many mL stand for ice?
1000 ÷ 100 = 10, and 70 × 10 = 700 mL.
3
What does scarcity mean?
There is not enough of something that people need.
4
Give two reasons why some people do not have enough safe fresh water.
Any two: drought, pollution, the water is hard to reach, there are not enough wells or pipes.
