Rainwater Harvesting for Lawn Irrigation: A Case Study in Diyarbakır Province

The prevalence of global water stress is rising annually as a consequence of population growth and industrialisation. The utilization of potable water from the drinking water network for irrigation, toilet flushing, and cleaning, which do not necessitate drinking water quality, exerts strain on freshwater resources. Consequently, the adoption of alternate water sources, such as rainwater harvesting (RWH) for non-potable applications, is becoming increasingly prevalent. This study investigates the potential of rooftop RWH to mitigate water stress in Diyarbakır, Turkey, by supplying irrigation water for lawns area. The research calculates the volume of rainwater that can be collected, filtered, and stored for irrigation, comparing it with the water needed to irrigate the lawn. The findings indicate that the potential for water savings is up to 55% when rainwater is collected on a 3600 m² roof area and used for irrigation on a 100 m² lawn area. In cases where the roof area exceeds 3600 m², the annual cash flow is consistently positive from the outset. Furthermore, it is important to note that the annual interest and inflation rates may vary from one country to another, which in turn affects the annual cash flow of the RWH system in each respective country. Moreover, the sum of the net present value (NPV) becomes positive only after 43 years. In the event that the storage tank and pump, which constitute the initial investment costs, are provided free of charge with the incentive, NPV is positive from the first year onwards. The study highlights that RWH can only achieve substantial water savings when there are extensive roof areas, thereby contributing to the alleviation of water scarcity in arid regions. Furthermore, the economic viability of RWH is contingent upon the provision of government incentives or subsidies.