Water

We use water every day for drinking, cooking, bathing, washing and cleaning, and much more water is used to grow crops and run industries. In this chapter you will estimate how much water a family uses and learn that we get water from ponds, lakes, rivers, wells and underground sources. You will study how water from oceans, rivers and the soil changes into water vapour by evaporation, and how plants also release water vapour through transpiration. As air rises and cools, the vapour condenses into tiny droplets that form clouds, and the water returns to the Earth as rain, hail or snow. This continuous circulation is called the water cycle. The chapter explains how rainwater flows back to rivers and seas and seeps into the ground to form groundwater. You will learn what happens when there is too much rain, causing floods, or too little rain for a long time, causing droughts. Finally, it discusses why water must be conserved and how rainwater harvesting, such as rooftop collection, helps recharge groundwater.

Detailed Worksheet: Water Section A - Definitions (10 marks) 1. What is evaporation? Name two places from where evaporation takes place. (2 marks) 2. What is transpiration? How does it add water vapour to air? (2 marks) 3. What is condensation? Give one daily-life example. (2 marks) 4. What is the water cycle? Name its main processes. (2 marks) 5. What is rainwater harvesting? Name one method. (2 marks) Section B - Calculations and Applications (15 marks) 6. A family of 4 uses water daily as follows: drinking 3 L per person, cooking 10 L, bathing 20 L per person, washing clothes 40 L and cleaning 15 L. (i) Find the total daily use. (ii) Find the use in a 30-day month. (iii) Suggest two ways to reduce it. (3 marks) 7. A tap leaks one drop every second, and 20 drops make 1 mL. (i) How many mL are wasted in an hour? (ii) How many litres are wasted in a day? (iii) Why should leaking taps be repaired quickly? (3 marks) 8. A rooftop of area 100 square metres receives 600 mm (0.6 m) of rainfall in a year. (i) Find the volume of rainwater falling on it in cubic metres. (ii) If 1 cubic metre = 1000 litres, how many litres is this? (iii) If 80 percent is collected, how many litres can be harvested? (3 marks) 9. Give the reason: (i) wet clothes dry faster on a sunny, windy day (ii) water droplets appear on the outside of a cold bottle (iii) a puddle disappears after a few hours of sunshine. (3 marks) 10. Explain the effects of (i) heavy rainfall for many days in a region (ii) no rainfall for one or two years (iii) cutting forests on the water cycle of an area. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the water cycle showing evaporation from the sea, transpiration from plants, condensation into clouds, precipitation, and flow of water back to the sea and into the ground. (4 marks) 12. Draw a labelled diagram of rooftop rainwater harvesting showing the roof, pipes, filter and storage tank or pit. (3 marks) 13. Draw a labelled diagram of the activity to show condensation, using a glass of ice-cold water or a cold plate held over boiling water. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Paheli kept two plates with equal amounts of water, one in the sun and one in the shade. (i) Which plate dried first? (ii) Why? (iii) Name two other factors that affect evaporation. (iv) How do salt makers use evaporation? (5 marks) 15. In many cities, groundwater levels are falling. (i) Why is groundwater important? (ii) Give two reasons for the fall in groundwater levels. (iii) How can rainwater harvesting help? (iv) Suggest two ways in which students can save water at school. (5 marks) 16. Only a small part of the water on Earth is fresh water fit for use. (i) Why can we not use sea water directly for drinking? (ii) Where is most of the fresh water found? (iii) Why is it important to conserve fresh water? (iv) How does the water cycle keep supplying fresh water? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw all diagrams neatly in pencil and label every part. Show all working for calculations.