Lithium Mining in the Salar de Atacama—Accounting Practices for Water Footprinting

As lithium demand increases, lithium brine from hyper-arid salt flats is becoming increasingly important, although there are concerns about its extraction’s impact on the local water balance. Water footprinting could address these impacts, yet studies lack consensus on whether to classify brine as water or a mineral. This study aims to review perspectives on lithium brine accounting within and beyond the water footprint context, focused on the Salar de Atacama, Chile, and to establish accounting principles for water footprinting, following the relevant ISO standard. Outside water footprinting, four perspectives on brine classification are identified: hydro-social/perceptual, molecular–thermodynamic, precautionary, and legal. Adopting some of these perspectives, e.g., the rationale of brine’s molecular–thermodynamic similarity to freshwater, some water footprint studies argue for accounting brine as equivalent to freshwater. However, they are a minority. According to ISO, brine should not be classified as freshwater, and the type of water and its functionality should be distinguished. We suggest some saline waters below a specific salinity threshold may function as freshwater and could be included in freshwater accounting. Additionally, lithium brine extraction can induce effects on surrounding water compartments. Since conventional water footprints overlook such local effects, we propose testing a set of site-specific accounting principles through case studies.