Using gray water footprint to verify economic sectors' consumption of assimilative capacity in a river basin: model and a case study in the Haihe River Basin, China

• A new approach to assess the consumption of assimilative capacity is presented.
• Case study in the Haihe River showed the largest gray water footprint in agriculture.
• Consumption observed in agriculture was largely driven by other sectors indirectly.
• Wastewater treatment is an effective way in sustaining assimilative capacity.

Assessing the consumption of assimilative capacity (AC) caused by wastewater discharge is an effective guide in the development of sustainable water use. Conventional studies only considered each economic sector's direct wastewater discharge as their consumption of AC, and ignored the indirect consumption of AC caused by the material-product flow network. In response to this problem, the concept of gray water footprint (GWF) was introduced to access the consumption of AC. An accounting method was also provided for GWF based on the input–output analysis (IOA) to deal with the indirect GWF connections between economic sectors. In a case study the GWF accounting method for China's Haihe River Basin was implemented. The results found that the total GWF was 3.35 × 1010 m3, of which 60.0% was for inhabitants and 40.0% was for exports. The GWF was larger than gross river flow and groundwater flow, highlighting an AC gap. This gap was consistent with the basin's water quality situation. The top three sectors with the largest GWFs were agriculture, wood (including paper and others), and chemical industry. The results showed that wastewater treatment helped to decrease the GWF by approximately 39%, which demonstrates the important effects of wastewater treatment and the need to improve wastewater treatment in these sectors. This study provides insights using assimilation capacity in the Haihe River Basin's current water challenge and is a reference for other basin studies.