A risk analysis and mitigation framework to reduce the impact of electricity disruption on water supply : based on a Cost vs Benefit analysis case study

Abstract

Mitigating the impact of electricity disruptions on water supply was investigated as a case study on the City of Tshwane. The case study was done based on a Risk Analysis and Mitigation Framework of Integrated Water and Electricity Systems, or RAMFIWES. This study includes (1) analysing the risks associated with water supply interruptions due to electricity disruption events, (2) proposing institutional and design guidelines to mitigate the impact of electricity disruption events to the various parties involved (electricity suppliers, Water Service Providers and Water Service Authorities), (3) estimating the cost of implementing various mitigating measures identified and (4) comparing this cost with the estimated economic benefit of ensuring uninterrupted water supply. Risk categories that were addressed are short-term disruptions of less than one day (for instance due to electrical maintenance with and estimated recurrence interval of 1 year), medium-term disruptions of up to a week (for example due to local distribution network failures as a result of vandalism or theft with an estimated recurrence interval of 20 years) and long-term electricity disruptions up to a month or even longer (for example due to a national blackout with a recurrence interval of 100 to 155 years). The direct economic benefit of ensuring uninterrupted water supply in the event of electricity disruption events were analysed through cost vs. benefit analyses. It was found that the direct benefit / cost ratio of supplying water during electricity disruption events is approximately 5.6 for wet-industries and 117 for other economic sectors in the City of Tshwane. The less easily quantifiable socio/political costs associated with longer duration wide area events are regarded to be much greater than the direct costs. The infrastructure required to ensure uninterrupted water supply during long-term electricity disruption events would result in an estimated increase of approximately 1% of the consumer’s water tariff. It should further be noted that installing the infrastructure to mitigate long-term electricity disruption events will also in turn mitigate all shorter duration electricity disruption events’effects on water supply will also be mitigated.