The prospects for rainwater harvesting at the University of Cape Town

Abstract

The viability of rainwater harvesting (RWH) as a fit-for-purpose water source for supply at the University of Cape Town (UCT) was investigated to reduce dependence on municipal water treated to unnecessarily high standards for purposes like toilet-flushing. Representative buildings on the UCT Upper and Middle Campuses, a parking area, and the tennis court on Upper Campus were identified as potential catchment areas. The ‘Yield after spillage’ (YAS) algorithm was used to identify the relationship between water demand and supply for various flush frequencies and storage sizes. The cost savings from harvested rainwater were estimated using the City of Cape Town (CoCT) 2021/2022 tariffs for Level 1 and Emergency Response water restrictions. A 20-year discount period and a 4% interest rate were used to determine the capital recovery amounts of the cost of ownership of the RWH systems. A multi-criteria analysis (MCA) tool that considered 3 weighting scenarios of the harvestable rainfall and economic viability was used to identify the most viable RWH systems. It was found that student residences could potentially reap the greatest benefits from installing RWH systems. Approximately 4 900 kLꞏyr⁻¹ and 4 000 kLꞏyr⁻¹ of rainwater can be harvested from Woolsack and Fuller Hall, respectively, if 100 kL tanks are provided, depending on the toilet flush frequency. The tennis court was identified as the most viable catchment for RWH. Approximately 7 500 kLꞏyr⁻¹ of rainwater could be harvested if 1 000 kL tanks are provided when the rainwater from the tennis court catchment is supplied to all Upper Campus buildings. It was also concluded that UCT is in a relatively good location for RWH due to its rainfall pattern as compared with those enjoyed by other universities across South Africa.