There is also an effort to shift from charging for irrigation water hased on the area covered to the volume of water used in many countries, especially where water stress is a serious issue. Policies regarding on-farm water resources, mainly groundwater, usually involve licenses and other regulatory instruments, but because of high transaction costs to enforce compliance, the degradation and illegal pumping of groundwater remains a challenge. To achieve sustainable groundwater use more effort will be required to enforce regulatory measures and develop mechanisms for volumetric management and charging, which is also essential for the management of surface water, especially where water stress is a serious issue. But achieving marginal cost recovery for groundwater supplies is complex, as is the development of groundwater markets.