What is a water footprint?
- The water footprint of a product is an empirical indicator of how much water is consumed, when and where, measured over the whole supply chain of the product.
- The water footprint is a multidimensional indicator, showing volumes but also making explicit the type of water use (evaporation of rainwater, surface water or groundwater, or pollution of water) and the location and timing of water use.
- The water footprint of an individual, community or business, is defined as the total volume of freshwater that is used to produce the goods and services consumed by the individual or community or produced by the business.
- The water footprint shows human appropriation of the world’s limited freshwater resources and thus provides a basis for assessing the impacts of goods and services on freshwater systems and formulating strategies to reduce those impacts.
Is the water footprint more than a nice metaphor?
- The term “footprint” is often used as a metaphor to refer to the fact that humanity appropriates a significant proportion of the available natural resources (land, energy, water).
- However, just like the “ecological footprint” and the “carbon footprint”, the “water footprint” is more than a metaphor: there is a rigorous accounting framework with well-defined measurable variables and well-established accounting procedures to calculate the water footprints of products, individual consumers, communities, nations or businesses.
How does the water footprint relate to ecological and carbon
- The water-footprint concept is part of a larger family of concepts that have been developed in the environmental sciences over the past decade.
- A “footprint” in general has become known as a quantitative measure showing the appropriation of natural resources or pressure on the environment by human beings.
- The ecological footprint is a measure of the use of bio-productive space (hectares).
- The carbon footprint measures the amount of greenhouse gases produced, measured carbon dioxide equivalents (in tonnes).
- The water footprint measures water use (in cubic metres per year).
- The three indicators are complementary, since they measure completely different things. Methodologically there are many similarities between the different footprints, but each has its own peculiarities related to the uniqueness of the substance considered. Most typical for the water footprint is the importance of specifying space and time. This is necessary because the availability of water highly varies in space and time, so that water appropriation should always be considered in its local context.
Why distinguish between a green, blue and grey
Freshwater availability on earth is determined by annual precipitation above land. One part of the precipitation evaporates and the other part runs off to the ocean through aquifers and rivers. Both the evaporative flow and the runoff flow can be made productive for human purposes.
The evaporative flow can be used for crop growth or left for maintaining natural ecosystems;
- The green water footprint measures which part of the total evaporative flow is actually appropriated for human purposes. The runoff flow – the water flowing in aquifers and rivers – can be used for all sorts of purposes, including irrigation, washing, processing and cooling.
- The blue water footprint measures the volume of groundwater and surface water consumed, i.e. withdrawn and then evaporated.
- The grey water footprint measures the volume of water flow in aquifers and rivers polluted by humans.
In this way, the green, blue and grey water footprint measure different sorts of water appropriation. When necessary, one can further classify the water footprint into more specific components. In case of the blue water footprint, it can be considered relevant to distinguish between ground and surface water use. In case of the grey water footprint, it can be considered valuable to distinguish between different sorts of pollution. In fact, preferably, this more specific pieces of information are always underlying the aggregate water footprint figures.