Another common water accounting error is to assume that ground and surface water systems are not connected to one another and to administer them separately. Many rivers play an important role in replenishing aquifers, while aquifers can provide much of a river’s base flow (Evans 2007). Failing to account for these interactions can result in the serious problems of over-use and degradation. One administrative solution is to reverse the onus of proof and require managers to assume that ground and surface water resources are linked and manage them as a single connected resource until such time as disconnection can be shown (NWC 2009).
Land-use changes can have similar effects on the volume of water available for use. For example, whenever a plantation forest is established, a hillside is terraced, or a farm dam is constructed, run-off is usually reduced. As a result, the quantity of water available for extraction from a river or aquifer is less than it otherwise would be. Accounting for water in a way that is consistent with the hydrological cycle and that avoids double counting of its potential is critical to developing the robust allocation and management systems that underpin a green economy (Young and McColl 2008).
2.3 Water and energy
The interdependence of water and energy demands also needs careful attention as arrangements are put in place for a transition to a green economy. There are at least two dimensions to this relationship.
First, water plays an important role in energy generation, notably as a coolant in power stations.
In the USA,
for example, 40 per cent of industrial water-use is for power-station cooling (National Research Council 2010), although water-use efficiency varies with the technology used (Figure 3). By 2030, it is expected that 31 per cent of all industrial water-use in China will be for cooling power plants (2030 Water Resources Group 2009). Generally, as countries become wealthier and more populous, industrial demand for water is expected to increase. In China, more than half of the increase in demand for water over the next 25 years is expected to result from a significant expansion in its industrial sector (see Figure 10), which will need to be accommodated through a simultaneous reduction in the amount of water used for irrigation in the agricultural sector.
Second, the water supply and sanitation sector is a large consumer of energy. Relative to its value, water is heavy and in energy terms expensive both to pump over long distances and to lift. In California, USA, where large volumes of water are transported over long distances, the water sector consumes 19 per cent of the state’s electricity and 30 per cent of its natural gas (Klein et al. 2005).
122
Nuclear OL Cooling
Fossil, biomass or waste - OL Cooling
Coal IGCC CL Tower
Natural gas CL Tower
Natural gas OL Cooling
Litres per MegaWatt/hour 5,300
2,000 350
Notes:
OL - Open Loop cooling CL - Closed Loop cooling
Figure 3: Water consumption for power
generation, USA (2006) Source: the U.S. Department of Energy (2006)