Design and Application of the Tank Simulation Model (TSM): Assessing the Ability of Rainwater Harvesting to Meet Domestic Water Demand

Abstract

Rainwater harvesting (RWH) is a necessary technology to supplement and/or replace insufficient ground and surface water resources for domestic water supplies, especially under changing climate conditions. An accessible and flexible Excel-based RWH simulation tool is developed and applied to investigate the utility of RWH in two regional case studies, under both present conditions and future climate scenarios, through examination of relationships between tank volumes, roof areas, rainfall patterns, and yield. The conversion of complex mathematical formula into a tool with a simple data entry form for infinite combinations of the critical variables enables non-experts to manipulate and optimize designs at the level of RWH implementation. The results clearly show that RWH can augment problematic or insufficient water supplies. Roof area and rainfall distribution have the greatest impact on the ability of a RWH system to meet demand; tank size has a minimal effect, providing a buffer during short dry periods within any given month. Demand met improves in both geographies under future scenarios. Thus, while RWH is insufficient as the sole source of domestic water now and in the future, it is a low-cost supply augmentation solution even in cold climates. RWH solutions are made more accessible through planning tools such as the Tank Simulation Model presented here, which is sufficiently flexible to incorporate climate change scenario planning.

Keywords: Canada, design tool, rainwater harvesting, rainfall patterns, reliability, Uganda, climate change scenarios