Cotton is the crop with the highest virtual water consumption in the world. Each year, cotton crops and the industrial processes to convert cotton into fabrics and to dye these fabrics require 256 Gm3 water.
To find out how this number is calculated, some concepts have to be borne in mind : The water footprint is defined as the total volume of water used to produce a product or service, and this includes :
"Blue water" : the amount of water supplied directly to manufacture the product, from regulated water sources (reservoirs, aquifers, water networks etc. ... ) .
"Green water" means rainwater naturally provided to the product.
"Gray water" the volume of water required to dilute to acceptable values the polluted water discharged after an industrial process.
The water footprint of a product is the addition of the water footprints generated at all stages of production of a product. In short: the water footprint is nothing other than the virtual water needed to produce a product
To be able to reduce the water footprint associated with the virtual water consumption of cotton-made fabrics it is necessary to take into account many variables. For example, there are significant differences in virtual water needed for cotton cultivation in different countries:
China: 4,545 litres of blue and grey virtual water per kg of cotton
Turkey: 5,936 litres of virtual water blue and gray cotton per kg
Turkmenistan: 19,942 litres of blue and gray virtual water per kg of cotton
If we understand that the planet has a unique water cycle, and that it is global, it is logical to produce each product in places where the process is more efficient in the use of water.
Cotton is a typical case of the export of virtual water. About 84 % of virtual water associated with cotton fabrics consumed in Europe is produced outside of this continent, and the environmental and economic impact of this consumption has consequences in producing countries (particularly in Asia) .
A suitable control of the cotton source can significantly reduce the virtual footprint of imports.
The second point to deal with is that when we talk about water footprint it is essential to study the process waters responsible for most of the grey water (caused by contaminated water requiring treatment).
Today, standard cotton fabrics’ production processes generate an average of 1,926 m3 of grey and blue waters per ton of fabric. However, a plant with good production techniques generates 1,180 m3 per ton and the best available techniques (Good Manufacturing Practice, GMP) allow a production with a footprint of only 522 virtual m3 per ton.
And there are still other factors to be considered, such as the particular environmental conditions of the producing areas, such as its water stress or natural value, the use of transgenic seeds, the possibility of replacing industrial crops for organic crops (of lower production, but less aggressive to the environment), socioeconomic factors that enable the adaptation of producers, etc. .
Cotton is a necessary product in our daily lives, therefore we must save as much water as possible. It is important to produce in countries where water consumption is more efficient and to find the best production systems where the virtual water is minimal. This is achieved when the levels of pollutants are close to zero because the grey virtual water required is minimal. Organic cotton is a material in the production of which no pollutants are used, the grey virtual water consumed being drastically reduced and, thus, the virtual water in general.