The rainwater harvesting potential of eZizityaneni and kwaNdela communities, Eastern Cape, South Africa

Abstract

The objective of the study is to determine rainwater harvesting (RWH) potential of the eZizityaneni and kwaNdela communities located in a rainfall-rich area of the Eastern Cape province of South Africa. Furthermore, the study aimed to determine the changes to the existing RWH-based water supply systems that would be required to fully supply the water demands if it cannot be achieved by the existing systems. Two households, a school and a clinic were selected as representative RWH users in the community. The study also aimed to compare financial viability between RWH-based water supply and traditional centralised municipal water supply system, and this was carried out for one household.

The study revealed that, with the existing RWH-based water supply system for two households that had storages of 10 and 15m3 , the level of supply at 96% statistical reliability is 250 and 280 days per year, respectively. However, if the storage capacity is increased to 45m3 for both households, the full supply of 365 days per year could be achieved at 96% statistical reliability. The study also reveals that, with the existing RWH-based water supply system for the clinic that has a storage of 15m3, the level of supply is 280 days per year at 96% statistical reliability, while increasing the storage size to 55m3 could achieve full supply at 96% statistical reliability. The existing RWH-based water supply system for the school with 27.5m3 storage can supply 86 days per year at 96% reliability and increasing storage to 90m3 could increase the supply to 132 days per year. Any further increase in storage cannot achieve a higher level of supply at 96% reliability and only an increase in roof area from the current 1246m2 could lead to higher levels of supply. It was found that the school can achieve full supply at 96% reliability with a roof area and storage size of 2250m2 and 380m3, respectively.

For the one household, where comparative life cycle cost analysis (LCCA) was carried out, it was found that installing a fully supplying RWH-based system would result in a payback period of 39 years if the cost of centralized municipal water supply is based on water tariffs which are typically highly subsidized. However, for LCCA based on the actual cost of centralized municipal water supply, the cumulative cost of RWH would be higher than that of municipal water supply for the first 14 years after which the cost of municipal water supply would escalate much faster to a cost that is 3.4 times higher than that of RWH by the end of the 50-year design life of the systems. The results suggest that while the communities could rely primarily on RWH-based water supply system, the system would be financially unattractive if not subsidized. The comparatively lower total life cycle costs of RWH than the municipal water supply reveals that subsidizing RWH-based water supply system may be the better of the two options for rainfallrich areas like the one in this study.