Water Footprint Manual: State of the art - A method of water footprint assessment by the Water Footprint Network (November 2009)

The concept is introduced as a comprehensive indicator of freshwater resources appropriation, as against the traditional and restricted measure of water withdrawal. The hidden water use behind products are measured over the full supply chain and water consumption volumes are measured by source and polluted volumes by type of pollution. All components of a total water footprint are specified geographically and temporally. Blue water (surface and groundwater), green water (rainwater stored in the soil as soil moisture) and grey water (polluted water) footprints are defined and are included along with the indirect water use in measuring the overall water footprints.

The core of the manual deals with the four distinct phases in water footprint assessment:

• setting goals and scope
• water footprint accounting
• water footprint sustainability assessment
• formulation of response

The goals and scope would vary for national governments, river basin authority, company etc. Water footprint accounts give spatio-temporally explicit information on how water is appropriated for various human purposes. The manual articulates the need for clarity about the inventory boundaries, about where to truncate the analysis, at what level of spatio-temporal explication and for which period of data when setting up a water footprint account. It in addition deals with difficult questions like whether to include the water footprint of labour, transport or energy applied in a production system in the assessment of the water footprint of the final product. 

The manual then goes on to state the inventory boundaries of water footprint sustainability assessment. The sustainability of a water footprint is viewed upon from different perspectives: the environmental, social and economic perspective. Besides, sustainability is measured at different levels: local (e.g. violation of local environmental flow requirements), catchment or river basin level (e.g. contribution to the violation of environmental flow requirements downstream). 

It presents complex equations explicating the water footprints due to processes and products and has sections dealing with calculation of:

• green, blue and grey water footprint of growing a crop or tree
• green and blue evapotranspiration using the CWR (Crop Water Requirements) option in the FAO’s CROPWAT model
• green and blue evapotranspiration using the ‘irrigation schedule option’ in the CROPWAT model.

You can directly download the manual here from the Water Footprint Network website.