Maheepala, S, Coultas, EH, Neumann, LE, Beal, CD, Stewart, R, Chong, MN and Sharma, Ashok ORCID: https://orcid.org/0000-0002-0172-5033 (2012) Quantifying potable water savings of rainwater tanks in South East Queensland by considering the spatial variability of tank supplies. In: The 3rd IWA_RWHM Conference, 20 May 2012 - 24 May 2012, Goeseong, Korea.

Abstract

Installation of domestic rainwater tanks is promoted as an alternative source of water supply in many Australian cities. Understanding the amount of water supply (i.e. yield) from rainwater tanks is essential for urban water supply planning, in particular to assess the long-term water supply security. This paper reports a study aimed at quantifying the yield from rainwater tanks in South East Queensland (SEQ), Australia by considering the spatial variability of tank supplies. The methodology involves Monte Carlo simulation of tank behaviour by considering the spatial variability of input variables, i.e. tank sizes, inflows to the tank, household water demand and losses associated with the tank inflow. Probability distributions have been used to represent the spatial variability of input variables except for the household water demand. The household water demand has been disaggregated into end uses. Water demand of the each end use has been simulated probabilistically to generate a plausible set of demand time series for each end use. These plausible demand time series have been used as an input variable to the rainwater tank simulation. Our method is different to the commonly used approach, which assumes that the yield of individual domestic rainwater tanks in a given area is the same for all the tanks and, that the tank characteristics and household water uses have linear relationships with the tank yield. The results have indicated that the error introduced to the average annual yield of a system with multiple rainwater tanks, by ignoring the spatial variability, can be of the order of 14%, if the tank is used for toilet flushing, clothes washing and garden watering. For single family residential households (i.e. detached dwellings) in SEQ, the rainwater tank yield found through stochastic simulation is 37 kilolitres/household/year, if the tank is used for toilet flushing, clothes washing and garden watering. This is of similar magnitude to the tank yield estimated from the billing data of the single family residential houses in the SEQ region. Further work is in progress to include a large sample of tank sizes and roof areas as well as water uses of both new and existing single family residential houses in Gold Coast, Ipswich and Sunshine Coast.

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