Rainwater harvesting is an ancient practice that involves collecting, storing, and using precipitation to meet on-site water needs. This paper develops and demonstrates guidelines for sizing the capacity of storage tanks to provide a reliable continuous supply of harvested rainwater for residential households. Operation of the rainwater harvesting system is simulated with a stochastic mass balance performed on an Excel spreadsheet. The daily volume of rainwater in an unbounded tank is tracked to determine the maximum accumulated deficit on a monthly basis. Results are summarized in dimensionless charts showing the minimum size of a rainwater storage tank needed to meet water demands at specified levels of reliability.
Martin, E. A., Buchberger, S. G., & Chakraborty, D. (2015). Reliability of harvested rainfall as an auxiliary source of non-potable water. In Procedia Engineering (Vol. 119, pp. 1119–1128). Elsevier Ltd. https://doi.org/10.1016/j.proeng.2015.08.954