However, this masks important variations across the globe-a lower share to agriculture in many highly industrialized countries and a much higher share in many lower income countries. South Asian countries, where British colonial rule invested heavily in large public irrigation systems (McGinn, 2009), stand out in particular with over 90% of freshwater withdrawn for agriculture (Figure 1), (World Bank, 2019). Consumptive use of irrigation water is less than 50% of the total volume diverted due to conveyance losses.As options for expanding water supplies dwindle across the globe, identifying opportunities for managing water demand gain importance (Chong & Sunding, 2006). Among these, water pricing (Molle & Berkoff, 2007) and approaches to reallocation non voluntarily through administrative decisions or voluntarily via collective decision-making or trade (Meinzen Dick & Ringler, 2008); emerge as central tools (Marston & Cai, 2016;Quentin Grafton et al., 2016;Richter, 2014). Among the many factors that can constrain water management (Marston & Cai, 2016), a fundamental constraint on the capacity to assess charges or make reallocations (whether voluntary or not) is the inability to measure water flow sufficiently and accurately. Volumetric water metering in agricultural systems is particularly challenging and broadly seen as impractical (Molle & Berkoff, 2007), so that in practice water fees are based often on cropped area, if they exist at all (