3 The distribution of water and its use by people
3.1 Water distribution and usage issues
People in many parts of the world currently face a chronic shortage of water. This is a developing crisis that is expected to get worse. As you read in Section 1, several factors underlie this dire prediction. In addition, climate change is expected to cause major changes in the distribution of freshwater. The uneven distribution of freshwater across the world is illustrated in Table 1.
Table 1 Distribution of the world's human population and available freshwater across six continents
|Continent||Proportion of world's||Proportion of world's|
|human population/%||available freshwater/%|
|North and Central America||8||15|
|Australia and Oceania||1||5|
From the data in Table 1, which continent is facing the greatest water crisis?
Asia. It contains nearly two thirds of the world's human population, but only one third of its available freshwater.
Generally, yes, it is. The regions of highest water availability (Asia, South America) have high rainfall. The region with the lowest water availability (Australia) has low rainfall.
People use water for a variety of purposes. As well as water for drinking, people use water to wash in, for sanitation, to irrigate the land for crops, to give to livestock, as a source of food (fishing), for transport and for recreation. The major categories of water use, on a global scale, are summarised in Figure 5, which shows that water use increased up to 1995 and how it is predicted to continue to increase up to 2025.
What is the most significant use of water worldwide?
Agriculture: in 2025 it will account for 60% of all the water extracted from natural water resources (just over 3000 km3 in the total of just over 5000 km3).
Which of the factors discussed in Section 1 account for the fact that water extraction is increasing?
Increasing human population and increasing per capita use of water.
Water use in agriculture is of two kinds: irrigation of crops and watering of livestock. Many methods of crop irrigation are wasteful of water in that much of it is lost into the air by evaporation before it is taken up by crops. Livestock use even more water. Table 2 compares the amounts of water required to produce various major food products. Notice how ‘expensive’ it is to produce beef and lamb in terms of water requirements.
Table 2: Volume of water required to produce 1 kilogram (kg) of specific food products
|fresh meat – beef||15 000|
|fresh meat – lamb||10 000|
|pulses, roots and tubers||1000|
The supply of clean water is affected by how people dispose of their waste water. People living in areas where there is no sanitation system for the disposal of waste water have little choice but to throw it away into a river or onto the ground. Each litre of water disposed of in this way pollutes an average of eight litres of freshwater, and the UN estimates that the global human population pollutes 12 000 km3 of water annually in this way. Unless there is major investment in sanitation systems, this figure will have increased to 18 000 km3 by 2050 (UNESCO, 2003).