Nomogram-based rainwater harvesting design for a sustainable residential water supply

Water scarcity is a critical issue exacerbated by climate change, urbanisation, and population growth, particularly in regions with insufficient water infrastructure. Rainwater harvesting (RWH) systems offer a sustainable solution to mitigate water shortages by collecting and storing rainwater for non-potable uses. This study focuses on the design, efficiency, and reliability of RWH systems in residential environments, with an emphasis on optimising the sizing of storage volumes and collection areas. Using a behavioural simulation model, we generate nomograms that facilitate the design of RWH systems by analysing the interactions among storage capacity, collection area, rainfall patterns, and water demand. Specifically, this paper evaluates the effectiveness of RWH systems through efficiency and reliability metrics such as water savings, mains reliance, overflow discharge, and system reliability. The proposed procedure integrates stochastic rainfall and water demand data, including a detailed analysis of toilet usage, to simulate the performance of RWH systems across different time scales. Case studies in Italy and Denmark are used to assess the influence of climatic differences on system performance. The findings provide a comprehensive methodology for RWH system design and offer valuable insights into improving a sustainable water management strategy.