GREY WATER FOOTPRINT OF CROPS AND CROP-DERIVED PRODUCTS: ANALYSIS OF CALCULATION METHOD

Abstract

The explosive increase in world population, along with the fast socio-economic development, have led to an increased water demand; the impact of global water resource consumption is mapped with the "water footprint", which is the total volume of freshwater used to produce the goods and services consumed. "Virtual water" is the volume of water used to produce a commodity, and is classified as green, blue and grey. "Blue water" refers to the volume of fresh water consumed along the supply chain of a product; "green" quantifies the volume of precipitation stored as soil moisture, and "grey" measures the volume of water required to dilute pollutants associated with a product's production chain to meet ambient water quality standards. When applied to agricultural crops, the calculation of grey water requires the following quantities: fertilizer application rate, crop yield, fertilizer leaching fraction, maximum allowed pollutant concentration in natural waters, and in the water where pollution is rejected. Much of this data is unavailable and researchers seem to proceed with a series of assumptions to calculate grey water figures. In this article, the common assumptions are reviewed, and prominence is given to weaknesses and the sensitivity of the calculation method.