Despite the most severe weather and geological conditions, Korean people in earlier times were successful in maintaining sustainable water supplies because they understood the importance of rainwater management, and developed technologies and a philosophy which were needed to live under such circumstances. Recently, the Korean people have suffered frequent incidence of flood damage and drought, and have gradually started to remind themselves of the lessons of the past, which can be described as proactive, multipurpose rainwater management. Most of the problems associated with water and energy can be solved by the integration of rainwater management practices. The concept of multipurpose rainwater management and two examples of its practice are discussed. One is a design for a multipurpose rainwater tank which has been used in a building project, and is based on Korean philosophy. Secondly, a regulation was promulgated recently in Seoul that requires the building of rainwater tanks in new buildings over a certain size. The primary purpose is for the prevention of flooding, but water conservation is a secondary intention. Two examples of proactive rainwater management are discussed, one being public involvement in rainwater management, and the second being the rainwater piggy bank microcredit project. In order to maintain sustainability, to meet the requirements of the Millennium Development Goals, and to be prepared for the effects of climate change, it is expected that multipurpose and proactive rainwater management will be a very effective approach for both developing countries and developed countries. A worldwide network of scientific researchers, as well as a great number of professions, has suggested the promotion of rainwater management.