Water Use Efficiency in Agriculture: From the Water Footprint Concept to Water Management Policies and Practices

The increasing global demand for food has led to an intensification of agriculture and to environmental consequences, including widespread overexploitation and pollution of freshwater resources. Furthermore, the increase in the extension of areas under irrigation and the higher water requirements of crops led to the development of indicators such as water footprint, water use efficiency, and irrigation efficiency to assess agricultural impacts on water resources. Water footprint of a product was defined to evaluate the water consumption, including rainwater (green water), surface, and groundwater (blue water) used by a crop during the growing cycle. The water sustainability use refers to blue water consumption as it determines the impact on water resources and competition with other activities. The concept of efficiency refers to the amount of output obtainable from a given amount of input, while the term “water productivity” concerns the outputs, that is, the economic value or other kinds of benefits that the outputs produce from the utilization of the water applied or consumed by the crop. The possibilities of improving the sustainability of water use vary to a great extent, from soil mulching to reduce unproductive soil evaporation, to conservation tillage and organic matter management to improve soil properties and the water-holding capacity, cultivation of drought-resistant crops or crop varieties to reduce vulnerability to water shortages, precision irrigation to maximize the fraction of irrigation water that reaches the plant, crop diversification and rotation to enhance resilience under water scarcity, to changing spatial cropping patterns to match crop choices to local growing conditions. Apart from representing an additional water source, the reuse of treated wastewater in agriculture can help expand water productivity to different extents and across different sectors (crop, economic, nutritional, and social), by generating multiple benefits from the same unit of water. When irrigation with wastewater is applied, a system that has the potential for nutrient recycling is created. The main issue of using wastewater is related to the presence of chemicals and microbes which, either directly or indirectly, can affect human and animal health by moving through the food chain; thus, the possibility of implementing wastewater for irrigation purposes requires treatments to reduce the risks of pathogens, heavy metals, and high salt levels.