Global water demand projections: past, present and future

Water demand projections (WDPs) are widely used for future water resource planning. Accurate WDPs can reduce waste or scarcity associated with overdevelopment or underdevelopment, respectively, of water resources. Considering that the projection period of some WDPs have now passed, this paper examines how closely such past projected withdrawals match current water withdrawals to identify lessons that can be learned and strengthen future studies on WDPs. Six WDPs conducted before 1990 and seven conducted after 1990 are analyzed in detail. The review shows that the pre-1990 WDPs, which considered population as the main driver of change, overpredicted current water use by 20 to 130%. Unrealistic assumptions on the norms of water use in different sectors were the main reasons for large discrepancies.