Water supply

In Chapter 1 we demonstrated that, at global and regional levels, water withdrawals do not exceed renewable resources, with often less than 10 per cent extracted. However, at a more local level, there is much more variability, such that in places consumption exceeds local supply. Such imbalances between supply and demand can be met through one of two possible responses: augment the (sources of) supply, or seek to reduce demand. In this chapter, we will focus on the fi rst of these alternatives (Chapter 6 will consider strategies to reduce demand). Figure 5.1 (similar to Figure 2.1 but here we display the relative proportions of water withdrawn rather than absolute amounts) shows that, globally, agricultural demand dominates water withdrawals. This is particularly pronounced in water poor regions, whereas in industrialised areas of Europe and North America municipal and industrial demand for water is much higher. As we showed in Chapter 1 (second section Water Scarcity: a Water Crisis, p.7), manufacturing industry is generally a more effi cient user of water than is agriculture. The different composition of demand means that, although industrialised countries have high levels of water consumption, heavy use of irrigation water means that in ‘less-developed’ Asia and the Middle East overall consumption fi gures are comparably high. Furthermore, in industrialised regions rates of withdrawal from renewable water resources are reduced through recycling and re-use of domestic and industrial effl uents and use of technology to augment natural water supplies. Where recycling is

concerned, we need to note that wastewater becomes effectively a new source of local ‘supply’, while also providing a means to reduce rates of abstraction from the wider water resources. To some extent, therefore, recycling may make it possible to sustain relatively high rates of individual water consumption while reducing environmental impacts.