Implementing rainwater harvesting systems as a novel approach for saving water and energy in flat urban areas

Abstract

Implementation of rainwater harvesting systems (RHS) is an effective approach to tackle increasing water and energy shortages for sustainable urban development. However, water and energy saving executions of RHS are rarely explored together in cities. This study explores the water and energy saving and economic performances of RHS in the four cities (Islamabad, Lahore, Peshawar, and Khanpur) under different climate zones of Pakistan. Three water demands (lawn irrigation, toilet flushing, and their mixture) were evaluated. Results indicated that higher annual water savings of RHS were associated with larger tank-sizes and lesser water demands in humid region. Differently, higher annual energy savings of RHS were related to greater energy consumption for groundwater pumping and larger tank sizes. At Islamabad, a 20 m³ RHS can achieve 126 m³ of annual water savings and 80% time reliability for mixed water demand, but only 23 m³ of annual water savings and 10% time reliability at Khanpur. At Lahore, a 20 m³ RHS can attain 119 kWh of annual energy savings for mixed water demand, but only 20 kWh at Khanpur. The economic viability of RHS was confirmed through adequately designed RHS at Islamabad, Lahore, and Peshawar, but except Khanpur due to its lower benefit-cost-ratio than 1.0.