What’s in a water footprint?

Freshwater resources – the increasing demand for, and increasing uncertainty of availability, have given rise to strong questions around water risks across agricultural value chains. The concept of water footprinting provides an effective platform from which to address and discuss these questions.

 

But what does a water footprint actually entail?

Water footprinting is a relatively new concept, initially coined by Arjen Hoekstra in 2002. While it has parallels with carbon footprinting, because of the localised context of water resources, there is more complexity embodied in its calculation.

Since the concept was initially established, two chief guidance standards have been developed in recent years: (1) The Water Footprint Assessment Manual, developed by Hoekstra et al. (2011); and (2) ISO 14046, developed by the International Organisation for Standardisation (ISO).

The Water Footprint Assessment Manual entails the calculation of a total water footprint according to the sum of three component footprints: green; blue; and grey water footprints:

  • The green water footprint refers to the ‘consumptive’ use of precipitation (before it becomes surface water). This water use is predominantly taken up by crop production, and its calculation is based on plant and soil evapotranspiration rates and historical precipitation across a plant’s growth cycle.
  • The blue water footprint refers to the consumptive use of surface water – water existing in rivers; dams; reservoirs; or groundwater bodies. At the farm level, the calculation of a blue water footprint is also based on plant and soil evapotranspiration rates. For processes different from that of agricultural production, the blue water footprint is a far simpler calculation.
  • The grey water footprint is calculated according to the volume of clean freshwater that would be required to dilute waste water (based on the volume, concentration and characteristics of the chief contaminant) to acceptable ambient levels (i.e. the assimilative capacity of local water bodies).

 

More recently, a water footprinting guidance standard has also been developed by the International Organization for Standardization – ISO 14046: Water footprint – Principles, requirements and guidelines. Although both guidance standards follow similar steps of assessment (defining the goal and scope of the study; building an inventory of water inputs and outputs; and assessing the impact of this water use on water resources), their methodologies differ considerably (ISO 2014).

Firstly, and most importantly, the ISO 14046 guidance standard is based on a water scarcity-weighted calculation, as opposed to purely volumetric (Hoekstra 2016). Secondly, the ISO 14046 standard does not directly account for the consumption of precipitation (green water under the WFN standard), which is rather accounted for elsewhere in a full lifecycle assessment. This has considerable implications for the calculation of a water footprint of agricultural products (Scheepers 2015; Munro 2015; Hoekstra 2016). Thirdly, under the ISO 14046 standard, the negative impacts on local water resources are assessed differently, based on an impact characterisation approach. But, ISO is still yet to prescribe impact characterisation methodologies – this process is therefore subjective and far from standardised.

 

Blue North is in the process of piloting a water footprinting data collection and assessment tool in the Western Cape stone fruit sector. On the basis of the above arguments, we have chosen to work with the WFN’s Water Footprint Assessment Manual, while drawing additional information from publically-available tools.

This is an interesting process for both Blue North and our clients – keep an eye on this space!

 

References

Hoekstra, A.Y., 2016. A critique on the water-scarcity weighted water footprint in LCA. Ecological Indicators, 66, pp.564–573. Available at: http://dx.doi.org/10.1016/j.ecolind.2016.02.026.

Hoekstra, A.Y. et al., 2011. The Water Footprint Assessment Manual, Available at: http://www.waterfootprint.org/?page=files/WaterFootprintAssessmentManual.

ISO, 2014. ISO 14046 Environmental management: Water footprint – Principles, requirements and guidelines,

Munro, S., 2015. A WATER FOOTPRINT ASSESSMENT OF PRIMARY CITRUS PRODUCTION IN THE LOWER SUNDAYS RIVER VALLEY CITRUS FARMS, EASTERN CAPE, SOUTH AFRICA. Rhodes University.

Scheepers, M.E., 2015. WATER FOOTPRINT AND THE VALUE OF WATER USED IN THE LUCERNE-DAIRY VALUE CHAIN. University of the Free State.