Spatial variability of reasonable government rebates for rainwater tank installations: A case study for Sydney

This paper presents the spatial variability of reasonable government rebates for rainwater tanks installations with a case study for the largest Australian city, Sydney. Five different rain-gauge stations are selected around different regions covering Sydney metropolitan area. An earlier developed daily water balance model (eTank) is used considering five average years' rainfall data as an input for each region. It is shown that significant variations among the regions are expected in regards to rainwater savings; even with the same tank size, same roof connection and same rainwater demand, south-east region saves more water than that of west and north regions. Also, region having lowest annual rainfall is not necessarily having lowest rainwater savings potential. Also, in regards to water savings efficiency, region having highest annual rainfall may not render highest water savings efficiency. Providing a double-sized tank or double sized roof is likely to increase the savings only up to 1.29 times. It is found that the payback periods of total rainwater tank related costs widely vary depending on region, tank, roof and demand scenario; a variation from 20 to 90 years without government rebate is expected. However, with reasonable government rebates these payback periods can be brought down to 8 years. To optimise government's spending a variable rebate scheme can be introduced based on the current findings.