The distinctive feature of the concept is that the volume of water consumed, evaporated, or polluted during production in the producing regions is related to the consumption of the produced goods domestically and elsewhere. This quickly shows that a great deal of water is used to manufacture goods in drought-affected developing countries for export to industrialized countries – water that is then lost to the local people and the domestic agriculture sector.
However, it's not just the volume alone that counts when assessing the water footprint. The type of water consumed also plays a role. This is categorized as follows:
Green water refers to the volume of rainwater that is stored in the soil. Plants absorb this water during their growth phase. However, the level of precipitation varies greatly depending on the climate zone and this vital resource is finite. Therefore, when consuming goods produced using lots of green water in regions with low rainfall, it's important to remember that this water can no longer be used to serve the needs of local people.
Blue water refers to the volume of water used in industry and domestically for artificial irrigation or the production of goods. This water comes from streams, rivers, lakes, or groundwater. Excessive use of these water resources always has an impact on the natural ecosystem and creates not only environmental but often also social and political problems.
Gray water refers to water that is so heavily polluted during production that it is rendered unusable for further use – whether as drinking water, in agriculture, or in industrial manufacturing. Such gray water has to be diluted with extremely large amounts of fresh groundwater to again meet the quality standards required for usage. Pest protection agents and fertilizers may cause such pollution. Unlike blue and green water, the term "gray water" relates to water quality.