Abstract
The purpose of this study is to compare the life cycle assessment and reliability of different rainwater harvesting (RWH) systems in residential buildings in Tehran for a period of 50 years. Four main scenarios based on the number of stories (1, 2, 3, and 4) each including five sub-scenarios based on the size of the rainwater storage tank (2.5m 3 , 5m 3 , 7.5m 3 , 10m 3 , 12.5m 3 ) and one using solely tap water were defined. Simapro software was used for life cycle assessment which was carried out using the endpoint and midpoint methods. The collected rainwater is assumed to be merely used to fill flush tanks and if it cannot satisfy this demand, tap water will be used. The results show that in an arid city like Tehran, collecting rainwater does not even come close to meeting non-potable water needs, and in most scenarios, tap water must be used for more than half of the days. Despite the low reliability of RWH systems, they perform better than tap water in most environmental impact categories because the processes used to produce tap water have the highest contribution to environmental damage. Among the sub-scenarios that use rainwater for flush tank demands, in almost all environmental impact categories, sub-scenarios that collect more rainwater (higher storage tank sizes) have better performance. The performance of sub-scenarios that use more rainwater is better in the endpoint environmental categories of ecosystems and human health; however, this trend is the opposite in the impact category of resources. Graphical abstract