Virtual water refers to the hidden volume of freshwater consumed or polluted during the production of a commodity or service. This volume is the total amount used throughout its entire supply chain, from raw material to final product, and is not the physical water contained within the item. The term was coined by Professor John Anthony Allan in the early 1990s. Understanding this embedded water volume is a foundational step in assessing how global consumption patterns impact limited freshwater resources worldwide.
The Hidden Reality of Virtual Water
Virtual water is often described as “embedded” or “indirect” water because it is consumed along the value chain but remains unseen by the end-user. The water used to irrigate crops, run industrial processes, or dilute pollutants never appears in the final product, distinguishing it from the direct water a person might use for drinking or washing.
The sheer volume of water required for common items highlights the significance of this hidden reality. Producing one kilogram of beef can require over 15,000 liters of water, with the majority of that volume going toward growing the animal’s feed. A single cup of coffee carries a virtual water footprint of about 140 liters, considering the cultivation and processing of the beans. Even non-food items, like a cotton shirt, require thousands of liters of water to grow the raw cotton fiber, manufacture the fabric, and dye the finished garment.
Breaking Down the Water Types
The total virtual water volume, or water footprint, of any product is comprised of three distinct components. The largest component is Green Water, which is the volume of rainwater stored in the soil that is evaporated or transpired by plants. This type of water is primarily relevant to agricultural, horticultural, and forestry products and represents about 74% of the global water footprint.
Blue Water represents the freshwater volume withdrawn from surface sources like rivers and lakes, or from groundwater aquifers. This water is used for irrigation, industrial processes, and domestic purposes, and it is considered a significant indicator of local water scarcity because it involves the direct consumption of finite resources.
Grey Water is the amount of freshwater required to dilute pollutants, such as fertilizers and pesticides, to acceptable water quality standards. Tracking these three types provides a comprehensive view of the resource’s origin and the impact on water quality.
Virtual Water and International Trade
The virtual water concept is a powerful tool for analyzing the flow of water resources through global commerce, known as virtual water trade. When a country imports water-intensive goods, it is effectively importing the virtual water used in their production, thereby conserving its own domestic water supplies. This strategy allows water-scarce nations to rely on products grown in water-rich regions, which can alleviate local water stress and support national food security.
The global flow of virtual water in international trade is substantial, estimated to be around 1,600 cubic kilometers per year, with agricultural products accounting for approximately 80% of this movement. Countries become net virtual water exporters when they ship out more embedded water than they bring in, while net importers are doing the opposite. Examining trade through this water lens offers a new perspective on environmental and economic sustainability, showing how consumption in one region is linked to water use thousands of miles away.