In the sustainability assessment step, we are assessing whether water use is balancing the needs of people and nature, if our limited water resources are being used to the greatest benefit and how fairly we are sharing the waters we use.
Environmental sustainability: To be environmentally sustainable, water use must not exceed the maximum sustainable limits of a freshwater resource. We use blue water scarcity to measure the environmental sustainability of the blue water footprint. It’s a measure of the blue water footprint compared to the water available after considering environmental flow requirements. When the blue water footprint is larger than the available water, environmental flows are not met and over time, freshwater ecosystems degrade.
When we consider the environmental sustainability of water use from the perspective of water quality, we compare the grey water footprint with the available assimilation capacity to measure the water pollution level. If the grey water footprint exceeds the assimilation capacity water quality standards are violated and the quality of the water will not meet socially agreed upon purposes.
Both of these, blue water scarcity and water pollution levels, are assessing the cumulative impact of all water uses of the freshwater resource. This can be done for sub-catchment or a local aquifer all the way up to large river basins and regional groundwater reserves.
Resource efficiency: The water footprint is an ideal measure of resource efficiency because it can be measured per unit of production, for example the cubic metres required to produce a ton of wheat. As the water footprint goes down, this indicates a more efficient use of water in producing the wheat or any other product. If the water footprint exceeds a benchmark of resource efficiency for that activity, this indicates that there is the opportunity for water footprint reduction through a change in practices or technology.
Equitable allocation: Unlike the carbon footprint, there are benefits to having a water footprint – the production of the food we eat, the clothes we wear, the materials used in building our homes, etc., requires there to be a water footprint. In addition to ensuring that the water footprint is environmentally sustainable and resource efficient, it also needs to be fairly shared amongst all people. This can mean that the allocation of the water footprint within a river basin is a fair allocation between different water users and different sectors in a way that benefits greater societal goals. It can also mean that no individual, community or country has a larger water footprint associated with the products and services they consume than others.