Study Guide on Water Footprint and Global Water Resources
INTRODUCTION TO WATER EVALUATION
This concluding chapter discusses emerging topics that may influence the global and regional assessment of water resources in the future.
The focus is particularly on the water footprint as a tool for understanding water use and flows worldwide.
The chapter emphasizes the importance of integrated water resource approaches, echoing themes from previous chapters in the book.
THE BASIC WATER FOOTPRINT CONCEPT
Traditional water use measures involve quantifying the amount of water withdrawn from surface sources (rivers, lakes) and groundwater, known as blue water.
These measures often overlook indirect water uses or the water needed to counter pollution caused by product manufacturing (known as grey water) and the water held in soil and vegetation (green water).
The water footprint concept was introduced by Hoekstra (2003), defining it as a nation's total use of global water resources, including:
Domestic water use
Net virtual water imports (water involved in the production of imported goods).
Virtual water, a term coined by Allan (1996), refers to the water used in the production of goods rather than referring to water that is simply 'an abstract concept'.
The water footprint concept parallels the ecological footprint by aggregating water usage across the supply chain and encompassing waste treatment.
The water footprint ultimately reflects human consumption patterns rather than production-associated demand within a country.
Research on water footprints connects global trade and water management and human consumption to overall water usage.
Water footprints can be calculated at different scales, including cities, companies, products, or individuals.
The total water footprint can be categorized into three components:
Blue water footprint: Water used from freshwater sources that doesn't return clean.
Green water footprint: Water stored in soil and vegetation, mainly from rainfall that is lost through evaporation and transpiration during crop growth.
Grey water footprint: The amount of water required to dilute pollutants to return the source to its original quality.
The total water footprint for a good, service, or product represents the sum of the three categories at a specific point in time.
Differences in definitions of grey water between water footprint studies and environmental management contexts should be noted.
EXAMPLES AND DATA ON WATER FOOTPRINT
Traditional metrics for water use mainly reflect blue water, which constitutes only about 3% of total consumption.
About 97% involves virtual water, with a significant portion coming from agricultural products (Chapagain and Orr, 2008).
A variety of products have their water footprints calculated (Mekonnen and Hoekstra, 2011, 2012). For instance:
Lettuce: 237 litres/kg – 77% green, 7% blue, 16% grey.
Milk: 1020 litres – 85% green, 8% blue, 7% grey.
Eggs: 3300 litres – 79% green, 7% blue, 13% grey.
Cotton (fabric): 10000 litres – 54% green, 33% blue, 13% grey.
Chocolate: 17196 litres – 98% green, 1% blue, 1% grey.
Coffee (roasted): 18900 litres – 96% green, 1% blue, 3% grey.
IMPLICATIONS OF WATER FOOTPRINT
The water footprint serves as a measurement tool for both freshwater use and water pollution.
It cannot provide an environmental impact assessment—understanding the effects of water usage is dependent on the catchment's vulnerability.
There’s no distinction between sustainable and unsustainable water use within the footprint, which could lead to misinterpretations regarding water scarcity across regions.
CALCULATING A WATER FOOTPRINT
Various methods exist for calculating water footprints, including:
Chain Summation Approach: Aggregates water use for a single output product across all production stages.
Stepwise Accumulation Approach: Used for products with multiple input sources, where water footprints of inputs are accounted for to determine the output product’s footprint.
Input-Output Model: A top-down perspective generally used for national or city-wide calculations, assessing end consumption.
Each method requires specific data on blue, green, and grey water usage, which can often be difficult to collect, particularly for grey and green water.
For products, water use is typically quantified in litres per unit produced, while consumer or company footprints are expressed in annual water use volumes.
Specific models exist to estimate the green water footprint based on variables such as soil moisture, type of crops, climate conditions, etc. (Fader et al., 2011).
EXAMPLE: CALCULATING THE WATER FOOTPRINT OF A SOFT DRINK
An example calculation is provided for a hypothetical sugar-containing soft drink, accounting for:
Direct Production Factors:
Blue water incorporated into the product: 0.50 litres.
Blue water consumed during production.
Grey water resulting from production.
Indirect Production Factors:
Recipes (ingredients) and packaging materials considered.
Supply Chain Factors:
Water used in energy and transportation involved in production.
Table of Water Footprint (litres) for a 0.5-litre PET bottle:
Component
Green Water
Blue Water
Grey Water
Total
Direct production
0.00
0.50
0.00
0.50
Direct supply chain (Sugar)
0.00-117.90
7.00-123.50
2.40-12.00
26.00-167.00
Other Ingredients
133.51
0.30
0.00
133.81
Packaging
1.034
0.256
6.0694
7.3594
Indirect supply chain
0.0012
0.005
0.7184
0.7246
Total (Min-Max)
134.55-252.45
8.06-124.56
9.19-18.79
168.39-309.39
THE GLOBAL WATER FOOTPRINT PICTURE
National water footprints indicate varying consumption levels, with American citizens consuming about twice the global average of water, while Chinese citizens consume approximately half the global average.
Global trade impacts water resources, as many developed countries rely on importing products that may stress water resources in developing nations.
Many African nations are net exporters of virtual water but still experience water shortages.
Water footprints must consider the dependency on imported resources and their impacts on local water availability.
VIRTUAL WATER FLOW AND ITS APPLICATION TO CHINA
A case study on China details the country’s challenge of meeting the consumption needs of approximately 1.3 billion people with limited freshwater resources.
North China faces severe water constraints with only 271 m³ available per person annually, leading to implications for agricultural production and water-intensive industries.
Trade data reveals significant export of virtual water from North China, predominantly through agricultural products.
Grey water accumulation from exports indicates environmental stress in regions producing water-intensive goods.
Comparatively, South China possesses more abundant water resources while importing some virtual water.
MOVING BEYOND THE STANDARD WATER FOOTPRINT
Expanding the concept of the water footprint to include assessments of disaster impacts (flood footprint) is suggested, as floods affect entire economies and ecosystems.
THE FUTURE OF WATER RESOURCES: AN INTEGRATED APPROACH
Water is vital for existence, impacting economies and societies.
The chapter underscores the need for cooperation amongst stakeholders, including scientists, policy makers, and local communities, to address water issues effectively.
Addressing the water crisis requires innovation in technology and decision-making strategies while ensuring equitable resource distribution.