Assessing the feasibility and effectiveness of rooftop rainwater harvesting in Winnie Mandela Madikizela Local Municipality

Abstract

South Africa's primary source of water is surface water. The potability of this water is doubtful especially in rural areas. Evaluation of rainwater quality from various roof materials is crucial. Additionally, there is a need to evaluate the quantity and the economic viability of Rooftop Rainwater Harvesting (RRWH). Winnie Madikizela Mandela Local Municipality (WMMLM) of Nomlacu currently has 73.6% municipal water supply backlog. With the current challenges, it is important not only to explore ways to save water but also to generate own sources of water. This makes RRWH systems as a viable water resource, an option for alleviating water scarcity. The study aims to assess the feasibility and effectiveness of RRWH for domestic use in WMMLM. The target is to determine the potential of rainwater harvesting as a potable water supply and conservation alternative. Hydrological data was obtained from the Weather SA to facilitate the calculation of the quantity of rainwater that can be harvested per household. Moreover, catchment areas were obtained through QGIS to determine size and materials of the roof types. Thus, to analyse the impact of roof materials on water quality for human consumption and irrigation. According to the results obtained in this study, Turbidity and E. coli produced noncompliant results of (0.8 – 2.8 NTU) and (0 - >2420 MPN /100mL) respectively. Although within limits, Aluminium, Colour, and Zinc concentrations present higher values on zinc metal roof compared to tiled roofing material. This is due to the high radiation and good heat conducting capacity of the metal. Results also showed higher pH levels on tiled roofs (7.05 – 7.39) compared to zinc roofs (6.27 – 7.19), which is in line with the nature of concrete. The most significant and immediate threat to health that roof collected water poses is bacterial contamination. Therefore, it is important to regularly clean the system, use disinfection solutions like chlorine tablets and boiling water before consumption. Overall, Nomlacu area receives relatively high amounts of rainfall which is greater than country’s annual rainfall. The study showed that RRWH can meet the annual demand of rainwater and have an overflow of roughly 7211L/year which is equivalent to an approximate potential annual harvest of 124% when utilized to its optimal potential and at worst case scenario can alleviate the pressure from the municipal water supply system by at least 81%. Results showed that optimal rainwater harvesting can be achieved by using more than two storage tanks per household. This then makes it possible for the system to alleviate pressure from the municipal water supply. On the economically aspect, installing a RRWH system is financially feasible, it would spare the municipalities approximately 48.8% of the municipal water supply spend to supply water to the municipality should this project be a government initiative.