Water Footprint
Authors: Aldaya Maite M. , Llamas M. Ramón , Hoekstra Arjen Y. 
Published: April 2017

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.

The water footprint concept broadens the scope of traditional national and corporate water accounting as it has been previously known. It highlights the ways in which water consuming and polluting activities relate to the structure of the global economy, opening a window of opportunity to increase transparency and improve water management along whole-production and supply chains. This concept adds a new dimension to integrated water resources management in a globalized world.

The water footprint is a relatively recent indicator. Created in 2002, it aims to quantify the effect of consumption and trade on the use of water resources. Specifically, the water footprint is an indicator of freshwater use that considers both direct and indirect water use of a consumer or producer. For instance, the water footprint of a product refers to the volume of freshwater used to produce the product, tracing the origin of raw material and ingredients along their respective supply chains. This novel indirect component of water use in supply chains is, in many cases, the greatest share of water use, for example, in the food and beverage sector and the apparel industry. Water footprint assessment shows the full water balance, with water consumption and pollution components specified geographically and temporally and with water consumption specified by type of source (e.g., rainwater, groundwater, or surface water). It introduces three components:

1. The blue water footprint refers to the consumption of blue water resources (i.e., surface and groundwater including natural freshwater lakes, manmade reservoirs, rivers, and aquifers) along the supply chain of a product, versus the traditional and restricted water withdrawal measure.

2. The green water footprint refers to consumption through transpiration or evaporation of green water resources (i.e., soilwater originating from rainwater). Green water maintains natural vegetation (e.g., forests, meadows, scrubland, tundra) and rain-fed agriculture, yet plays an important role in most irrigated agriculture as well. Importantly, this kind of water is not quantified in most traditional agricultural water use analyses.

3. The grey water footprint refers to pollution and is defined as the volume of freshwater that is required to assimilate the load of pollutants given natural concentrations for naturally occurring substances and existing ambient water-quality standards.

The water footprint concept has been incorporated into public policies and international standards. In 2011, the Water Footprint Network adopted the Water Footprint Assessment Manual, which provides a standardized method and guidelines. In 2014, the International Organization for Standardization adopted a life cycle-based ISO 14046 standard for the water footprint; it offers guidelines to integrate water footprint analysis in life-cycle assessment for products. In practice, water footprint assessment generally results in increased awareness of critical elements in a supply chain, such as hotspots that deserve most attention, and what can be done to improve water management in those hotspots.

Water footprint assessment, including the estimation of virtual water trade, applied in different countries and contexts, is producing new data and bringing larger perspectives that, in many cases, lead to a better understanding of the drivers behind water scarcity.