An international review of the market, current practices and R&D projects on the topic of rainwater harvesting management was performed. The review highlighted leading countries in different regions of the world, but also the variety of practices and acceptance. Current R&D issues and further research needs are identified and discussed. The application of RWHM techniques at household level seems to be mature, but sanitary risks exist when rainwater is used inside homes and also reserve on economical an environmental aspects can be drawn when drinking water supply is available. Promising concepts are being developed and demonstrated at larger scale such as industrial or commercial buildings or even urban catchments where the use of rainwater and the operation of the systems are under full control. For schemes of this scale, the integration and optimization of several beneficial aspects such as –traditionally- additional water supply and stormwater management, but also urban planning with water and green spaces, energy compensation in buildings and in the cities or ecological enhancement seems to be promising. Specific expertise will be required to best plan these schemes according to the local conditions and targets and to operate, maintain and upgrade them over their entire life time.

Rainwater Harvesting (RWH) is the process of collecting and storing rainwater for a later use. This technique could be an alternative water source in response of a climate change context. In this review, the state of this practice worldwide was studied. Some discrepancies between countries have been highlighted. First, between developed and developing countries, gaps concerning techniques and regarding the main purposes (water savings for the first ones and drinking purposes for the last ones) were reported. Then, within developed countries themselves, acceptance and standards of RWH installations are different, with precise guidelines and norms for countries leading the way on RWH practices. The scale of applications (RWH for households – up to 50 inhabitants, for large buildings and for urban area) is discussed and the state of the technique showed that there were more potential of technological development and challenges for large scale systems than for households. Finally, this report draws the attention to the needs in terms of Research and Development projects. Six main aspects were highlighted: drinking water, energy compensation, environmental impacts, economical aspects and the integration of stormwater management and rainwater harvesting. The last feature concerns hygienic aspect, but the report do not focus on this consideration.