The paper summarizes the implementation experiences and lessons learned from the solar water heating (SWH) system mandatory installation policy in China. In-depth interviews, questionnaire surveys and field investigation were conducted to understand the prevailing attitudes of the stakeholders associated with the application of SWH in buildings. Scenario analysis was used to analyze the effect of expanding the coverage of mandatory installation policies. The results show that due to the strong market externalities of SWH building applications, the government must provide inducements to stakeholders through mandatory policies or fiscal incentives to create an impetus for them to use SWH extensively. For China, it is necessary to strengthen and support the utilization of renewable energy policies and extend the mandatory installation policy of SWH systems to taller buildings to fulfill the national renewable energy application goals. The most reasonable technical route, full process control, and attention to system operation and maintenance are the three key factors for the successful implementation of a mandatory installation policy for SWH systems. The policy recommendations presented in this paper can not only be applied to China but also other developing countries as well.