Approximately 15–18 billion m3 of freshwater resources are contaminated by fossil fuel production every year.
Waterborne transit is one of the most energy efficient means of transport. Inland towing barges are more than three times more energy efficient than road trucks and 40% more efficient than rail. As transportation is one of the most energy intensive sectors in the urban context, increasing the use of waterways for passenger or goods transit can lead to substantial energy savings.
Wastewater contains energy in the form of potential energy, thermal energy and chemically bound energy, all of which can be harnessed and utilized. In the USA, there are 104 wastewater treatment plants using biogas to produce a total of 190 MW capacity. Wastewater is increasingly recognized as potential source of energy: in several countries, water supply companies are working towards becoming energy-neutral. It is estimated that more than 80% of used water worldwide -and up to 90% in developing countries- is neither collected nor treated, threatening human and environmental health.
There are currently more than 16 000 desalination plants worldwide, with a total global operating capacity of roughly 70 million m3 per day. Desalination is the most energy-intensive water treatment technology: desalinated water involves the use of at least 75.2 TWh per year, which is about 0.4% of global electricity consumption.
Energy is required for two components of water provision: pumping and treatment (before and after use). Electricity costs are estimated at 5% to 30% of the total operating cost of water and wastewater utilities, but in some developing countries such as India and Bangladesh, it is as high as 40% of the total operating cost.
Geothermal energy is climate independent, produces no GHG emissions, does not consume water, and its availability is infinite at human time scales.
The demand for agricultural feedstock for biofuels is the largest source of new demand for agricultural production in decades, and it was a major factor behind the 2007−2008 spike in world commodity prices.
Although hydropower generation is a major water user, most of the water used is returned to the river downstream even though it is in part consumptive (reservoir evaporation) and has important impacts on other attributes of streamflows (timing and quality). However, the benefits of hydropower generation do not always flow to the people who depend on rivers for their livelihoods.
Hydroelectricity is currently the largest renewable source for power generation in the world. Hydropower’s share in total electricity generation is expected to remain around 16% through 2035. In Latin America and the Caribbean, hydropower provides some 65% of all electricity generated (even more in Brazil, Colombia, Costa Rica, Paraguay and Venezuela); the world average is 16%.
Thermal power plants are responsible for roughly 80% of global electricity production. Power plant cooling is responsible for 43% of total freshwater withdrawals in Europe, nearly 50% in the USA, and more than 10% in China.