When diving into a water footprint sustainability assessment, many different questions and issues can arise. In some assessments, the complexity of scope and scales require the development of unique and innovative water footprint sustainability assessment approaches.
Sustainability assessment and response formulation can seem a hard and complex task when the geographic scope spreads across multiple locations in different rivers basins all over the world. The question of where to start working and how can feel hard to answer.
The results of the water footprint accounting and the sustainability assessment can help unravel these complexities. They can be used to prioritise the locations where the water footprint lands and can lead to identifying the most appropriate response options in a coherent way. This provides guidance on where to start working to achieve sustainable water use by using the framework of Water Footprint Assessment.
This method establishes which river basins or regions should be prioritised, based on the analysis of three components: the size of the water footprint, geographic hotspots and process efficiency.
The priority basins are those that have a significant share of the water footprint (e.g. > 1%) and are in a geographic hotspot and/or exceed the benchmark.
Response formulation is also guided by the outcome of the sustainability assessment. The decision tree below shows the process whereby the results can be used to whether to take action individually or collectively, within a specific sector or across a combination of sectors. Working through this decision tree establishes the strategic actions required for river basins where the water footprint is located.
In situations in which resource efficiency benchmark’s are already being met and the water footprint is located in a geographic hotspot, it is often strategic to work collaboratively with others to reduce the overall basin water footprint to maximum sustainable levels. In other situations, the solution may be fully within the control of the individual’s operations, such as improving the quality of wastewater released from a factory or using better technology in-house.
Conducting a Water Footprint Assessment at a fine scale, i.e. including all sub-catchments in a catchment area for surface and groundwater, explicitly shows the variations of water consumption and pollution in space and time. It presents clear evidence of the relationship between water quantity and water quality, and forms a basis for integrated water resource management.
Water quantity and water quality regulations are often developed independently of each other and are sometimes managed by different institutions or departments within a single institution. This means that the links between water availability and water quality are often not recognized or managed through the regulations on water abstraction and emissions’ permits.
In order to properly assess these relations in a catchment and contribute to an adequate regulatory system, the assessment needs incorporate all factors holistically, such as multiple water use sectors (industrial, domestic and agricultural), different sources of water (surface and groundwater) and different types of human pressure on water resources (consumption and
pollution). The spatial and temporal resolution required to highlight the linkages between these factors needs to be defined according to the specific scope of work.
Water footprint accounting is undertaken by applying the definitions and formulae set in the Water Footprint Assessment Standard. For this type of assessment, it is necessary to consider both surface and ground water in blue and grey water footprint accounting, so we focus on how this should be addressed.
The total blue water footprint in each sub-catchment will be the blue water footprint of surface water of all processes in the sub-catchment, plus the blue water footprint of groundwater of all processes in the sub-catchment.
Likewise, the grey water footprint in each sub-catchment will include the grey water footprint of surface and ground water. In grey water footprint accounting it is necessary to include pollution loads from point sources of water pollution (when pollutants are directly released into a surface water body in the form of a treated or non-treated wastewater disposal), and diffuse source pollution (e.g. agriculture). For the grey water footprint of groundwater, the applicable groundwater quality standards should apply when determining maximum allowable concentrations.
The water footprint sustainability criteria used for this assessment are the blue water scarcity and the water pollution level. These are related to blue water footprint and grey water footprint respectively – the environmental sustainability indicators commonly applied in Water Footprint Assessment.
The water footprint sustainability assessment is carried out using blue water scarcity, water pollution levels and water footprint hotspots. Hotspots occur where the blue water footprint is larger than the blue water availability of the area and/or where the grey water footprint exceeds the assimilation capacity for water pollution of the area, therefore indicating that the blue water footprint and/or the grey water footprint are unsustainable, respectively.
According to the Water Footprint Assessment Standard, blue surface water scarcity is defined as the ratio of the total of blue water footprint in the catchment to the blue water availability of the catchment. Water pollution level is defined as the fraction of the waste assimilation capacity consumed. It is calculated by taking the ratio of the total grey water footprints on surface water in a catchment to the actual runoff of that catchment.
Blue surface water availability is quantified by the difference between the natural run-off in the catchment and the environmental flow requirement. However, how can we determine blue ground water availability?
Blue groundwater availability can be approximated by the sustainable yield. The sustainable yield has been discussed and elaborated in a range of studies 1, 2, 3. The sustainable yield concept has evolved from the safe yield concept. However, there is not yet a common consensus on one definition of the sustainable yield. Nevertheless, it is generally regarded as the amount of groundwater that could be abstracted without exceeding the natural recharge or harming the groundwater system from environmental, economic, or social considerations, in a long-term perspective 4, 5.
Applying a Water Footprint Assessment, including all sub-catchments in a catchment area, for surface and groundwater explicitly shows:
Such information is fundamental to form the basis for integrated water resource management in the catchment area. Regulatory agencies should aim for demand management within the constraints required to meet sustainability criteria, such as blue water scarcity and water pollution levels, and recognise the relationships between them. When combined, these response strategies can lead to an overall improvement in the sustainability of water use in catchments.
An example is the creation of a decision logic incorporating the three phases of water footprint accounting, water footprint sustainability assessment and response formulation. This sets up a system whereby the current status of the environmental criteria of blue water scarcity and water pollution levels for surface and groundwater indicate whether additional abstraction licences or discharge permits should be approved and with which conditions (see diagram below). If implemented, this approach would guide regulatory agencies in reaching sustainable water use and management.