Life cycle costing of rainwater tank as a component of water sensitive urban design

Water conservation has become a major issue in Australia in recent times. Additional fresh water supplies are constantly being sought after and rainwater tanks are emerging as a possible solution. Studies have previously focussed on water saving potential of rainwater tanks used in domestic applications but little research has been undertaken on larger multi-storey applications. This paper presents an investigation of the life cycle cost analysis of a 75kL rainwater tank in a hypothetical multistorey residential building in Sydney. An Excel based model was developed and sixty years of rainfall data were considered to determine potential water savings based on different scenarios including varying roof areas and number of floors. A sensitivity analysis was performed based on varying water prices and discount rates. The most favourable scenario for a rainwater tank of 75kL size was found to be at a water price of A$1.634/kL, a 5% nominal discount rate and 4.5% inflation for water price, which presented a payback period of 38 years.