There is nothing wrong with a plant or a crop that uses a lot of (rain)water while it grows, with the condition that the environment in wich it grows isn’t negatively impacted. In other words: when the region has a water supply (through rain for example) that is equal to the amount consumed by the plant, there really is no problem. Problems arise when crops consume so much water that rivers, lakes or underground aquifiers run dry. A high water footprint often indicates, but not always, a high water footprint impact. Some components of the water footprint can have negative environmental impacts, but other components may be without any problem. Besides, it deserves consideration whether one has a total water footprint below or beyond one’s equal share of the available freshwater resources in the world.
For consumers it would be helpful to integrate a water label in broader labels that include other issues as well, such as energy and fair trade. Ideal would be a world in which we do not need labels because we can trust that all products meet strict criteria. If a water label is considered, the question is what should be on the label. One could put the total water footprint of the product on a label, which is functional only for raising awareness among consumers, not for enabling the consumer to make a well-informed choice between two products. For supporting good product choice, one would also need to specify the green-blue-grey components and mention the degree in which the product’s water footprint relates to violation of local environmental flow requirements or ambient water quality standards. For example, three quarters of the water footprint is situated in areas where environmental flow requirements or ambient water quality standards are met, but the other quarter of the total water footprint is in areas where those norms are violated.
So in the end, labelling of products is a partial solution at best. As a means of raising awareness it can be functional, but it is just one way of providing product transparency, restricted by the practical problem that a label can contain limited information only. Besides, real water footprint reduction will not occur just by providing information on a label.
Water footprint per kilo is a dubious measurement. We eat very different quantities of food, and their concentration of useful nutrients differ widely. If we look at use of blue and green water per calorie, nuts has the lowest efficiency in water use and root crops are the best. Vegetables and meat are quite similar. Looking at blue and grey water use per protein, oil crops are best followed by milk, lamb, root crops and grain. Nuts and vegetables are the least efficient.
The aggregate water footprint of a product, consumer or producer shows the total volume of fresh water consumed and/or polluted. It serves as a rough indicator, instrumental in awareness raising and for getting an idea of where most of the water goes. The water footprint can be presented as one aggregate number, but in fact it is a multidimensional indicator of water use, showing different sorts of water consumption and pollution.
Another point of discussion is where to draw the end of a supply chain of a product. For example, does the waterfootprint of the fuel needed for transport also be incorporated? Or the waterfootprint of the truck that is used for transport? Maybe the water footprint of the driver? Some of these arguments are more valid than others but it shows that water footprint concept isn’t perfect.