Tradable water right systems are becoming important ways to achieve distributive efficiency in water resources. In 2002, China's Ministry of Water Resources initiated a pilot project in Zhangye City in Northwest China. The project was designed to establish a new water use rights system with tradable water quotas with the hope of reallocating water resources more efficiently through market-based instruments. However, the tradable water right system is not well enforced. Based on both primary and secondary data, we find that mutual monitoring can improve the effectiveness of a water allocation and trading program. For both surface water and groundwater irrigation systems, the conditions needed to stimulate mutual monitoring include: (1) a hierarchical management system; (2) well defined water rights or quotas; (3) control of total water quotas and water sources by the upper hierarchy; and (4) an approximate balance between the water supply or pumping capacity and the water quota. We describe also the institutional requirements for stimulating mutual monitoring.