We need water in our daily life at any time. The amount we consume is far more than that we see, because a large quantity of water is hidden in products or food. "Water footprint" is thus an indicator of water use that refers to the total volume of freshwater directly and indirectly used to produce goods and services.
"Water footprint" seems to be an abstract concept, but when we review the whole process of producing an item, various examples of virtual water could be found: 1. Water sourced from rivers or lakes by humans 2. Water from precipitation stored in plants, which have been in taken by humans or animals 3. Water used to assimilate pollutants from the production of goods
Perhaps you are familiar with "carbon footprint" (the amount of carbon dioxide emission caused by humans). "Water footprint" also allows us to be aware of the impact of our daily life to water resources. For example, you could not image how much water is required to produce one piece of steak...
Source: Water Footprint Network