Water footprint of drinking water: The consumptive and degradative use

Abstract

Centralized water supply systems provide an essential service for society, although they generate direct and indirect environmental burdens to water resources. Quantifying the environmental aspects and impacts is paramount to improving the sustainability of water supply systems, especially in regions affected by water scarcity. In this context, this study aimed to assess the water footprint (WF) of drinking water production. In the aspect dimension, the water footprint assessment (WFA) was used to account for the direct and indirect consumptive (WFBLUE) and degradative (WFGREY) uses of freshwater in m3FW, summed in a WFCOMBINED indicator. Additionally, in the impact dimension, the water scarcity footprint (WSFBLUE) was used to assess the consumptive use of freshwater equivalent in m3 world-eq. The functional unit was 1.0 m3 of drinking water produced in a water treatment plant (WTP) located in northeastern Brazil. Primary data from the water utility company was used in the foreground inventory. The system boundary covered the WF flows for water extraction from the reservoir, net difference of evaporation-to-precipitation on the reservoir surface, supply of chemicals and electricity, WTP infrastructure, transport, WTP sludge management, and water incorporation in the final product (i.e. water content in drinking water). Aside from the Base scenario, where the raw sludge is discharged into the surface water body without treatment, four proposed scenarios for sludge management were evaluated. The WFA results showed that the WFCOMBINED was 67.7 m3FW per m3 of drinking water in the Base scenario, in which direct WFGREY (97.4 %) was the major contributor due to the aluminum assimilation from the sludge discharge, followed by direct and indirect WFBLUE (1.7 %), mainly due to the water incorporation into the final product, and indirect WFGREY (0.9 %). The direct WFGREY in the Base scenario was highly sensitive to the coagulant dosage. The sludge management measures in the proposed scenarios were landfill disposal (Scenario 1), landfill cell sealing material (Scenario 2), recycling in the production of ceramic goods (Scenario 3), and treatment for coagulant recovery (Scenario 4), which reduced the WFCOMBINED by at least 97 %. The coagulant recovery scenario presented the smallest WFCOMBINED and the highest level of compliance with the current environmental standard and policy. The WSFBLUE was obtained using the Available WAter REmaining (AWARE) method considering different method versions and spatiotemporal coverages. The WSFBLUE was highly sensitive to the characterization factor used, which led to different impact rankings when comparing with other regions of the world from the consulted literature. Multiple WF indicators were used herein to represent water consumption, water degradation, and water scarcity, showing how they support more robust decision-making in water resources planning, management, and security.