A revised water footprint method devised by Ridoutt and Pfister takes into consideration the type of water source and different usages during stages of production to determine how much Dolmio® pasta sauce and Peanut M&M’s® contribute to water scarcity (2009). Existing water footprint calculations use the volumetric summation of all water content in the product at all stage of production and consumption. Under the existing method, the products Dolmio® pasta sauce and Peanut M&M’s® have water footprints of 202 and 1153, but the revised water footprints offer a drastically different relationship. The stress-weighted water footprints of Dolmio® pasta sauce and Peanut M&M’s® are 141 and 131. Winnie Wong
Ridoutt, B., Pfister, S., 2010. A revised approach to water footprinting to make transparent the impacts of consumption and production on global freshwater scarcity. Global Environmental Change 20, 113-120.
Bradley G. Ridoutt of the Australian Commonwealth Scientific and Research Organization and Stephan Pfister of the Swiss Federal Institute of Technology Zurich demonstrated a revised water footprint calculation method using brand products, Dolmio® pasta sauce and Peanut M&M’s®. Ridoutt disaggregates water according to the different sources: blue water which is surface and groundwater sources, and green water which is rainwater that is consumed through crop evapotranspiration. Because some places have a higher degree of water scarcity than others, location and level of stress imposed by different activities are considered in calculating a product’s water footprint. Therefore, the water consumption at specific locations at each point in the product life cycle and the water stress index (WSI) by Pfister (2009) were used to determine the level of contribution to water scarcity of both products.
In both cases of Dolmio® pasta sauce and Peanut M&M’s®, the agricultural stage of production contributed the greatest, followed by operations, ingredients processing and packaging. The study found that blue water sources are typically directly consumed at rates exceeding short-term replacement therefore processes heavily using blue water sources contributes significantly to stress-weighted water footprints. A main ingredient of Dolmio® pasta sauce is tomato. Due to the stress-heavy consumption of blue water in agriculture, tomatoes contributed more than 95% of stress-weighted water footprint. Therefore, efforts to reduce water footprint should focus on stress-heavy processes and not necessarily processes that use more water.
The study argues that the simplistic existing volumetric method is unequipped to accurately depict how production impacts water scarcity. This method is misleading and confusing as these water footprints do not accurately reflect a product’s impact on the water supply. A revised water footprint method would allow quantitative comparisons between products in terms of potential to contribute to water scarcity. Water footprint assessment methods need to accurately reflect the impact of consumption and this requires a revised approach that considers the incorporation of water stress characterization factors. The revised method will help corporations direct optimal actions to reduce negative impact of water supply and help consumers to make more informed purchases.