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Water conservation

Water is a very precious substance and yet far too often, earth's water resources are abused and taken for granted. How many times have you walked past polluted rivers and streams, or seen the flow of water in a river reduced to almost nothing because of its extraction for industrial and other uses? And if you were able to test the quality of the water you see, you would probably be shocked. Often our water resources are contaminated with chemicals such as pesticides and fertilisers. If water is to continue playing all the important functions that were discussed earlier, it is vital that we reduce the impact of humans on these resources.

Group work : Human impacts on the water cycle

Read the following extract from an article, entitled 'The Effects of Urbanisation on the Water Cycle' by Susan Donaldson, and then answer the questions that follow.

As our communities grow, we notice many visible changes including housing developments, road networks, expansion of services and more. These changes have an impact on our precious water resources, with pollution of water being one of many such impacts. To understand these impacts you will need to have a good knowledge of the water cycle!

It is interesting to note that the oceans contain most of earth's water (about 97%). Of the freshwater supplies on earth, 78% is tied up in polar ice caps and snow, leaving only a very small fraction available for use by humans. Of the available fresh water, 98% is present as groundwater, while the remaining 2% is in the form of surface water. Because our usable water supply is so limited, it is vitally important to protect water quality. Within the water cycle, there is no 'new' water ever produced on the earth. The water we use today has been in existence for billions of years. The water cycle continually renews and refreshes this finite water supply.

So how exactly does urbanisation affect the water cycle? The increase in hard surfaces (e.g. roads, roofs, parking lots) decreases the amount of water that can soak into the ground. This increases the amount of surface runoff. The runoff water will collect many of the pollutants that have accumulated on these surfaces (e.g. oil from cars) and carry them into other water bodies such as rivers or the ocean. Because there is less infiltration, peak flows of stormwater runoff are larger and arrive earlier, increasing the size of urban floods. If groundwater supplies are reduced enough, this may affect stream flows during dry weather periods because it is the groundwater that seeps to the surface at these times.

Atmospheric pollution can also have an impact because condensing water vapour will pick up these pollutants (e.g. SO2, CO2 and NO2) and return them to earth into other water bodies. However, while the effects of urbanisation on water quality can be major, these impacts can be reduced if wise decisions are made during the process of development.

Questions

  1. In groups, try to explain...
    1. what is meant by 'urbanisation'
    2. how urbanisation can affect water quality
  2. Explain why it is so important to preserve the quality of our water supplies.
  3. The article gives some examples of human impacts on water quality. In what other ways do human activities affect water quality?
  4. What do you think some of the consequences of these impacts might be for humans and other forms of life?
  5. Imagine that you are the city manager in your own city or the city closest to you. What changes would you introduce to try to protect the quality of water resources in your urban area?
  6. What measures could be introduced in rural areas to protect water quality?

Apart from the pollution of water resources, the overuse of water is also a problem. In looking at the water cycle, it is easy sometimes to think that water is a never-ending resource. In a sense this is true because water cannot be destroyed. However, the availability of water may vary from place to place. In South Africa for example, many regions are extremely dry and receive very little rainfall. The same is true for many other parts of the world, where the scarcity of water is a life and death issue. The present threat of global warming is also likely to affect water resources. Some climate models suggest that rising temperatures could increase the variability of climate and decrease rainfall in South Africa. With this in mind and remembering that South Africa is already a dry country, it is vitally important that we manage our water use carefully. In addition to this, the less water there is available, the more likely it is that water quality will also decrease. A decrease in water quality limits how water can be used and developed.

At present, the demands being placed on South Africa's water resources are large. Table 1 shows the water requirements that were predicted for the year 2000. The figures in the table were taken from South Africa's National Water Resource Strategy, produced by the Department of Water Affairs and Forestry in 2004. In the table, 'rural' means water for domestic use and stock watering in rural areas, while 'urban' means water for domestic, industrial and commercial use in the urban area. 'Afforestation' is included because many plantations reduce stream flow because of the large amounts of water they need to survive.

Table 1: The predicted water requirements for various water management areas in South Africa for 2000 (million m33/annum)
Water management area Irrigation Urban Rural Mining and bulk industrial Power generation Afforestation Total
Limpopo 238 34 28 14 7 1 322
Thukela 204 52 31 46 1 0 334
Upper Vaal 114 635 43 173 80 0 1045
Upper Orange 780 126 60 2 0 0 968
Breede 577 39 11 0 0 6 633
Country total 7920 2897 574 755 297 428 12871

Case Study : South Africa's water requirements

Refer to Table 1 and then answer the following questions:

  1. Which water management area in South Africa has the highest need for water...
    1. in the mining and industry sector?
    2. for power generation?
    3. in the irrigation sector?
    4. Suggest reasons for each of your answers above.
  2. For South Africa as a whole...
    1. Which activity uses the most water?
    2. Which activity uses the least water?
  3. Complete the following table, by calculating the percentage (%) that each activity contributes to the total water requirements in South Africa for the year 2000.
    Table 2
    Water use activity% of SA's total water requirements
    Irrigation 
    Urban 
    Rural 
    Mining and bulk industry 
    Power generation 
    Afforestation 

Now look at Table 3, which shows the amount of water available in South Africa during 2000. In the table, 'usable return flow' means the amount of water that can be reused after it has been used for irrigation, urban or mining.

Table 3: The available water yield in South Africa in 2000 for various water management areas (million m33/annum)
Water management area Surface water Ground Irrigation Urban Mining and bulk industrial Total local yield
Limpopo 160 98 8 15 0 281
Thukela 666 15 23 24 9 737
Upper Vaal 598 32 11 343 146 1130
Upper Orange 4311 65 34 37 0 4447
Breede 687 109 54 16 0 866
Country total 10240 1088 675 970 254 13227

Case Study : Water conservation

Refer to Table 3 and then answer the following questions:

  1. Explain what is meant by...
    1. surface water
    2. ground water
  2. Which water management area has the...
    1. lowest surface water yield?
    2. highest surface water yield?
    3. lowest total yield?
    4. highest total yield?
  3. Look at the country's total water requirements for 2000 and the total available yield.
    1. Calculate what percentage of the country's water yield is already being used up.
    2. Do you think that the country's total water requirements will increase or decrease in the coming years? Give a reason for your answer.
  4. South Africa is already placing a huge strain on existing water resources. In groups of 3-4, discuss ways that the country's demand for water could be reduced. Present your ideas to the rest of the class for discussion.

Summary

  • Water is critical for the survival of life on Earth. It is an important part of the cells of living organisms and is used by humans in homes, industry, mining and agriculture.
  • Water moves between the land and sky in the water cycle. The water cycle describes the changes in phase that take place in water as it circulates across the Earth. The water cycle is driven by solar radiation.
  • Some of the important processes that form part of the water cycle are evaporation, transpiration, condensation, precipitation, infiltration and surface runoff. Together these processes ensure that water is cycled between the land and sky.
  • It is the microscopic structure of water that determines its unique properties.
  • Water molecules are polar and are held together by hydrogen bonds. These characteristics affect the properties of water.
  • Some of the unique properties of water include its ability to absorb infra-red radiation, its high specific heat, high heat of vaporisation and the fact that the solid phase of water is less dense that its liquid phase.
  • These properties of water help it to sustain life on Earth by moderating climate, regulating the internal environment of living organisms and allowing liquid water to exist below ice, even if temperatures are below zero.
  • Water is also a good solvent. This property means that it is a good transport medium in the cells of living organisms and that it can dissolve gases and other compounds that may be needed by aquatic plants and animals.
  • Human activities threaten the quality of water resources through pollution and altered runoff patterns.
  • As human populations grow, there is a greater demand for water. In many areas, this demand exceeds the amount of water available for use. Managing water wisely is important in ensuring that there will always be water available both for human use and to maintain natural ecosystems.

Summary Exercise

  1. Give a word or term for each of the following phrases:
    1. The continuous circulation of water across the earth.
    2. The change in phase of water from gas to liquid.
    3. The movement of water across a land surface.
    4. The temperature at which water changes from liquid to gas.
    Click here for the solution
  2. In each of the following multiple choice questions, choose the one correct answer from the list provided.
    1. Many of the unique properties of water (e.g. its high specific heat and high boiling point) are due to:
      1. strong covalent bonds between the hydrogen and oxygen atoms in each water molecule
      2. the equal distribution of charge in a water molecule
      3. strong hydrogen bonds between water molecules
      4. the linear arrangement of atoms in a water molecule
      Click here for the solution
    2. Which of the following statements is false?
      1. Most of the water on earth is in the oceans.
      2. The hardening of surfaces in urban areas results in increased surface runoff.
      3. Water conservation is important because water cannot be recycled.
      4. Irrigation is one of the largest water users in South Africa.
      Click here for the solution
  3. The sketch below shows a process that leads to rainfall in town X. The town has been relying only on rainfall for its water supply because it has no access to rivers or tap water. A group of people told the community that they will never run out of rainwater because it will never stop raining.
    Figure 1
    Figure 1 (CG10C6_007.png)
    1. List the processes labelled P1 and P2 that lead to rainfall in town X.
    2. Is this group of people correct in saying that town X will never run out of rainwater? Justify your answer using the sketch. Recently, the amount of rainwater has decreased significantly. Various reasons have been given to explain the drought. Some of the community members are blaming this group who told them that it will never stop raining.
    3. What scientific arguments can you use to convince the community members that this group of people should not be blamed for the drought?
    4. What possible strategies can the community leaders adopt to ensure that they have a regular supply of water.
    Click here for the solution

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