First, for financial sustainability to be respected, a nonmarginal number of users will have to pay more than the long-term average cost of service provision. A second key aspect is the capacity of the structure to appropriately target the poor, defined by Komives et al. ( This tariff structure does not qualify as a social tariff as it has not been established that poor households consume much less water than more well-off ones: empirical research tends to indicate that income elasticity of water demand is low, in other terms, the poor do not necessarily consume less water than the rich.