Analysis of Stormwater Harvesting Potential: A Shift in Paradigm is Necessary

Abstract

With increasing population and changing climate regime, water supply systems in many cities of the world are under stress. Water demand is increasing day by day but resources of fresh water are limited. To tackle the situation many water authorities around the world have been promoting the use of water conservation and recycling options through various campaigns and offering incentives/grants for such water saving ideas and innovations. Even with several educational and awareness campaigns and financial incentives, there is a general reluctance to adopt any potential stormwater harvesting measure. The main reasons behind this are that people are not aware of the payback period for their initial investment and the optimum size of the storage required satisfying their performance requirements. Among all the alternative water sources, stormwater harvesting perhaps has received the most attention. One of several water conserving techniques is on-site stormwater harvesting for non-drinking purposes. However there is a lack of knowledge on the actual cost-effectiveness and performance optimisation of any stormwater harvesting system, in particular the proposed design storage volume could be overestimated or underestimated. At present stormwater harvesting systems are proposed and installed without any in-depth analysis of its effectiveness in various climate conditions.The biggest limitation of stormwater harvesting schemes and designs is the rainfall variability, which will control the size of the storage needed. Furthermore, with the impacts of global warming and potential climate change, climate variability is expected to increase more. The traditional practice of rainwater harvesting volume/size design is based on historic annual average rainfall data. However, design of rainwater harvesting volume based on annual average rainfall data is not realistic. As a stormwater harvesting system designed considering average rainfall will not provide much benefit for a critical dry period. An in-depth analysis considering different climate regimes (dry, average and wet years) is necessary. A user-friendly tool, eTank was developed to make end-users’ decision making process easy, effective and knowledgeable. This chapter presents several case studies within Melbourne (Australia) using eTank for the purpose of rainwater tank optimisation. Outcomes of the case studies are presented in the form of cumulative rainwater saved under different climatic conditions (dry, average and wet years).