(Introduction)
Concept of peak oil
Comparison of water and oil
Are we running out of water?
Renewable vs. nonrenewable resources
Consumptive vs. non-consumptive uses
Transportability of water
Substitutes for oil and water
Climate change
Utility of the term “Peak Water”
Fossil groundwater
“Peak Ecological water”
A new water paradigm: The soft path for water

『Conclusion
　As the world anticipates a resource-constrained future, the specter of “peak oil” - a peaking in the production of oil - has been predicted. Similarly, many in the news media have been referring to new limits on the availability of water, which some have termed “peak water.” There are important differences between water resources and oil resources. Oil production will inevitably decline, while water uses within renewable limits can continue indefinitely. Oil is a finite, non-renewable resource that is consumed during its use; therefore, oil production will inevitably decline. Peak oil, thus, means the end of cheap, easy-to-access sources of petroleum. Any new sources of liquid fuel will be harder to reach and more expensive to extract. Water is a renewable resource and is not consumed in the global sense; therefore, water uses within renewable limits can continue indefinitely. Oil is routinely transported over long distances from extraction to use, making it a global resource. Conversely, water cannot be economically transported over long distances, making it primarily a local resource. These characteristics mean that there is a global limit to oil production; constraints on water are only manifested regionally. And while many water uses can be reduced or eliminated, a basic amount of water is necessary for life to exist and for which, unlike oil, there are no substitutes.
　Despite the serious limitations in the concept of “peak water,” as described in this chapter, there are some interesting and valid applications. Not all water use is renewable; indeed some water uses are non-renewable and unsustainable. Groundwater use beyond normal recharge rates follows a peak oil type curve with a peak and then precipitous decline in water production.
　Considering the multiple roles that water provides as the fulcrum foe ecosystems as well as human society, we suggest that the term “peak ecological water” better delineates an important crisis in the water sector. As human appropriation of water increases, the ecological services that water provides decrease. Once we begin appropriating more than “peak ecological water,” ecological disruptions exceed the human benefit obtained. Defined this way, many regions of the world have already surpassed “peak ecological water” - humans use more water than the ecosystem can sustain without significant deterioration and degradation.
　Another resonance in the concept of “”peak water』 is that similar to peak oil it signals the end of cheap and easy to access water. This recognition of the value of water can help drive towards an important and needed paradigm shift in the way water is managed and priced. In this way, the concept of “peak water” helps moves us towards using water in ways that improve the productivity, equity, and efficiency of water use.
　What is exciting about the concept of “peak water” is that it may be an additional impetus for a new “soft path for water” paradigm to emerge. In places where peak water is a reality, managers are moving to recognize and manage water as a valuable and precious resource. True limits on regional water availability can also stimulate innovations and behaviors that can reduce water use and increase the productivity of water. Though the use of “peak water” is flawed in key ways, it shifts us in the direction of protecting and preserving precious water resources - a necessary step for a sustainable water future.

References
Box 1.1. The origins of water on Earth