Handbook of Water Harvesting and Conservation

26Rainwater Harvesting Storage-Yield-Reliability Relationships

John Ndiritu

University of the Witwatersrand, South Africa

26.1 Introduction

Rainwater harvesting (RWH) from roofs or other impervious surfaces for on-site use is a common source of water supply in many regions of the world. However, decisions on storage sizing and assessments of the yield and reliability of supply in many regions are not based on the comprehensive hydrologic analysis that is typically applied to larger centralized water supply systems (McMahon and Adeloye 2005; Basson et al. 1994). Design and operational decisions of centralized water resource systems are usually based on in-depth studies conducted by the responsible authorities or consultants, but RWH is often installed by individuals or entities that do not have the skills to conduct detailed hydrological analysis or the resources to involve specialists. Consequently, simplified methods based on monthly average rainfalls are sometimes used or recommended (Handia et al. 2003; Abdulla and Al-Shareef 2009; Denison et al. 2011) and RWH users are at times uncertain about the capabilities of their systems (Thomas et al. 2014). The optimization of system sizing is also considered a requirement for effective RWH development (Duncker and Matsebe 2015). Although RWH systems are often regarded as backup supply in many countries, they also serve as primary water sources in several countries of the world (Campisano et al. 2017). If RWH serves as a primary ...