Assessment of diurnal water demand patterns to determine supply reliability of plumbed rainwater tanks in south east queensland

Understanding the impact of rainwater tanks on household diurnal water demand patterns for new residential dwellings in South East Queensland is important for water system design. In this study, water demand patterns for 20 Class 1 residential dwellings with internally plumbed rainwater tanks in South East Queensland (SEQ), were monitored from April-August 2011. The monitored parameters included total mains water use, mains top-up to rainwater tanks and total water drawn from rainwater tanks for internal and external purposes. Preliminary results show that the total average household water demand for these dwellings was 133 Litres/person/day, which is significantly lower than the reported average water demand of 153 Litres/person/day for the same period, across the SEQ region. An assessment of the daily diurnal water demand pattern for the cluster-of-20 households revealed two water demand peaks; one each for the morning and evening. The mean volumetric reliability of the mandated rainwater tanks across the individual households was found to be 26%, which is the ratio of the rainwater available in the rainwater tank system to the total household water demand during the monitoring period. Subsequent water balance analysis on the dynamics of rainwater tanks found that the rainwater source alone could offset the peak hour water demand by 28%, with a daily average offset of 10%. The monitoring activity will be extended into the future to take seasonal effects into account. The findings from this study would provide information that would be significant for the future of urban water resources management in SEQ.