How to Predict the Financial Prospects of a Rainwater Harvesting System——An Innovative Approach Based on Catchment Fraction

Abstract

Rainwater harvesting (RWH) systems are one of the most promising technologies for water supply and economic viability is often a major barrier to their implementation. In order to develop a generic method to assess the economic viability of decentralized RWH systems at a regional level, this paper investigates the effect of variations in building characteristics on the economic performance of rainwater harvesting systems in regions where the water tariffs and rainfall distribution characteristics are fixed. This paper simulated the financial efficiency (expressed as a benefit-cost ratio) of a large number of decentralized RWH systems in Guangzhou, China. It is found that the financial efficiency of RWH systems is closely related to the catchment fraction (the ratio of rainfall catchment surface to total floor area). Based on this dimensionless parameter, explicit equations expressing the financial efficiency of RWH systems were derived using a nonlinear regression method. In addition, the validity of the analytical equations was verified by the root mean square error test, normality test, and error distribution test. This analytical solution provides a simple and generic method for forecasting the investment potential of rainwater harvesting systems. The developed methodology can also be adapted to other regions merely the variations of local water price and rainfall data need to be considered.