The water cycle

Question 1

Describe the water cycle (3)

Answer 1

• precipitation (water reaching the ground)
• evaporation (changes from liquid to gas)
• condensation (gas to liquid)

repeats

Question 2

Describe precipitation

Answer 2

water vapour in clouds cools to form rain/snow which then falls to the ground

Question 3

Describe evaporation

Answer 3

some water evaporates after falling as precipitation

some water runs into water sources

some water gets stored in aquifers

water evaporates from water sources (seas) and from plants when they transpire

Question 4

Describe condensation

Answer 4

water vapour rises after evaporation into the clouds

as it rises it cools and condenses

Question 5

potable water

Answer 5

water which is safe to drink

Question 6

How is water made potable?

Answer 6

• treated with chemicals and filtered
• dirt, pathogens, and toxic substances (e.g. metal ions) are removed
• in areas of drought, water is taken from the air or salt water sources

Question 7

desalination

Answer 7

• hot climates without much precipitation can produce drinking water from salt water using desalination (removing the salt)
• one method is distillation

Question 8

Explain how distillation can be used to produce potable water in a village that is close to the sea [4]

Answer 8

• salty water is heated until it evaporates, forming steam
• the steam is condensed in another container to give pure water
• the salt and other impurities are left behind in the salty water
• if renewable energy (e.g. sunlight) is used this saves electricity costs and avoids pollution

Question 9

disadvantages of desalination

Answer 9

• the water needs to be heated until it evaporates, this requires a lot of energy and so is very expensive
• only removes soluble impurities, some harmful substances will remain (although anything living will be sterilised by the heat)

Question 10

Describe the processes that take place in the water cycle [5]

Answer 10

• water evaporates
• forms clouds
• condenses into precipitation/rain
• runs off land into rivers
• is taken up by plants
• filter through ground
• then more evaporation and the cycle continues
• evaporates from ground, water surface or transpiration

Question 11

Suggest the effect on the water cycle of planting a large number of trees [3]

Answer 11

less water available in rivers as it is taken up by trees for photosynthesis

less precipitation due to less evaporation from river

less water in rivers/aquifers/drier soil