Water is a unique resource in that it is essential to life and irreplaceable. The water cycle is a critical Earth-system process that human activity is beginning to alter. Water availability varies significantly across the globe. There is an abundance of water in some places, and extreme shortages in others. This regionality has led to some debate as to the existence of a global limit for water.
The regional variability of water scarcity does not mean that water is not a global commodity. Water used directly by a consumer is only a small proportion of her total water use. Water is also used indirectly in the production of goods and services as “virtual water”. Approximately 40% of the water consumed in Europe is virtual water. It is not a rational argument to suggest that those in water-rich locations need not be concerned about water consumption as much of the water they consume is likely to be from other locations.
The Planetary Boundary for water is only for blue water, i.e. it excludes the use of green water (rainwater) and grey water (contaminated water). Blue water consumption is a reasonable proxy indicator with which to understand the state of the world’s water assets. However, the Planetary Quota for water needs to be in a unit that makes sense across different scales of human activity. As such, the use of green water and production of grey water are both relevant and important. Further, the Planetary Boundary for water considers gross water consumption. The level of water treatment now available is such that net water consumption is substantially lower than gross water consumption. It is also more relevant to planetary health.
There is no consensus as to a global water budget for net blue, green, and grey water. However, some argue that even at current consumption rates many of our global water bodies are under stress suggesting that the upper limit cannot be higher than current consumption rates.
Thus, the Planetary Quota for water is net water (blue, green, and grey water) ≤8500 km3. This limit is set based on the current global water footprint and can be compared to the water footprint of any scale of activity.
- AMTA (2016) Membrane desalination power usage put in perspective. America’s Authority in Membrane Treatment, Stuart, FLGoogle Scholar
- Falkenmark M (1986) Fresh water—time for a modified approach. Ambio 15:192–200Google Scholar
- Leahy S (2018) From not enough to too much, the world’s water crisis explained. National Geographic, National Geographic SocietyGoogle Scholar
- Mekonnen MM, Hoekstra AY (2011b) National water footprint accounts: the green, blue and grey water footprint of production and consumption. Value of water research report series no. 50. UNESCO-IHE, DelftGoogle Scholar
- Molden D (2007) Comprehensive assessment of water management in agriculture. International Water Management Institute, Earthscan, LondonGoogle Scholar
- Pitt C (2018) Cape Town water consumption drops by 43 million litres. news24. news24Google Scholar
- Porada B (2012) Virtual water imports and exports by regionGoogle Scholar
- Raskin P, Gleick P, Kirshen P, Pontius GA, Strzepek K (1997) Water futures: assessment of long-range patterns and problems. In: SEI (ed) Comprehensive assessment of the freshwater resources of the world. SEI, StockholmGoogle Scholar
- Rockström J, Gordon L, Folke C, Falkenmark M, Engwall M (1999) Linkages among water vapor flows, food production, and terrestrial ecosystem services. Ecol Soc 3:5Google Scholar
- Rockström J, Steffen W, Noone K, Persson A, Chapin FS, Lambin E, Lenton TM, Scheffer M, Folke C, Schellnhuber HJ, Nykvist B, De Wit CA, Hughes T, Van der Leeuw S, Rodhe H, Sorlin S, Snyder PK, Costanza R, Svedin U, Falkenmark M, Karlberg L, Corell RW, Fabry VJ, Hansen J, Walker B, Liverman D, Richardson K, Crutzen P, Foley J (2009) Planetary boundaries: exploring the safe operating space for humanity. Ecol Soc 14:32CrossRefGoogle Scholar
- Secretariat of the CBD (2001) Global biodiversity outlook 1. In: SotCoB (ed) Diversity. UNEP, CBD, MontrealGoogle Scholar
- Shiklomanov IA (1993) Water in crisis: a guide to the world’s fresh water resources. In: Gleick P (ed) Oxford University Press, New YorkGoogle Scholar
- Steffen W, Richardson K, Rockström J, Cornell SE, Fetzer I, Bennett EM, Biggs R, Carpenter SR, De Vries W, De Wit CA, Folke C, Gerten D, Heinke J, Mace GM, Persson LM, Ramanathan V, Reyers B, Sörlin S (2015) Planetary boundaries: guiding human development on a changing planet. Science 347:1259855CrossRefGoogle Scholar
- UN (2015) The human right to water and sanitation. UN, GenevaGoogle Scholar
- Wangnick Consulting (1990) IDA worldwide desalting plants inventory. International Desalination Association, Englewood, NJGoogle Scholar
- WWF, WWL (2014) Freshwater: what’s at stake, what we’re missing, what we’re losing, what it’s worth. http://wwf.panda.org/about_our_earth/about_freshwater/importance_value/. Accessed 27 Mar 2014