Towards a green economy ■ The volume of water available per person in a region;
■ The efficiency of water supply in the urban sector and water use;
■ The efficiency of water use in the agricultural and industrial sectors; and
■ The water use and water related impacts of companies and countries.
1.5 The world’s water resources Access to the world’s water resources is heavily dependent upon the nature of the water cycle. While a massive amount of water reaches the earth’s land surface, much less, around 40 per cent, makes its way into creeks, rivers, aquifers, wetlands, lakes and reservoirs, before cycling back into the atmosphere (see Figure 1). Of the water that is extracted for human purposes, on average, approximately:
■ 70 per cent is used for agricultural purposes;
■ 20 per cent is used by industry (including power generation); and ■ 10 per cent is used for direct human consumption.
Given that the vast majority of usable fresh water is channelled towards agriculture, any global consideration of water allocation must consider the factors that determine the efficiency of water use in the sector. Irrigated land produces around 40 per cent of the world’s food (Hansen and Bhatia 2004; Tropp 2010). One of the biggest challenges facing water managers is to find a way to significantly increase the productivity of irrigated agriculture so that water can be transferred to other sectors without adversely affecting the environment or food security. In many parts of the world there are few opportunities to enhance supplies at reasonable cost.
But general observations can be misleading. No two water bodies are the same. Managing large, complex, trans- boundary water systems typically requires a different approach to overseeing smaller water systems, where local issues are often all that need to be considered. In developing countries, water management and investment are typically geared towards reducing poverty and enabling economic development;
the priority for developed nations tends
to be maintaining infrastructure and supplying access to water at reasonable cost. In both cases, there is a need to focus more on long-term sustainability of the systems and services provided. Demand and supply also vary greatly. In Singapore, for example, almost all water is extracted for urban and industrial purposes, while in many other parts of the world, the majority of water is extracted for agricultural or mining purposes (Cosgrove and Rijsberman 2000).