Evaluation of plumbed rainwater tanks in households for sustainable water resource management: a real-time monitoring study

In recent years, there has been a significant emphasis placed on achieving reductions in urban residential water demand through the application of alternative water resources on various housing development scales based on a “fit-for-purpose” concept. One such resource is rainwater that could be used in various non-potable applications at household level in urban areas. Savings in mains water achieved through the inclusion of rainwater as a source for residential use are plausible; however, analyses on quantifying the actual reduction in mains water demand are still at an early stage to incorporate into strategic planning for urban water supply. This paper highlights the real-time monitoring outcomes of 20 detached households with plumbed rainwater tanks in an attempt to assess their volumetric reliabilities, diurnal water demand patterns and water energy nexus. The rainwater usage (or mains water saving) was validated and assessed using 12 months monitoring data and an average yearly rainwater usage of 40 kl/household was found. The volumetric reliability, which is the ratio of the rainwater usage to the total household water demand, was found to be on average 31%. The instantaneous peak water demand was estimated to range between 16 and 93 l/min within the monitored homes, which has a strong implication for the design of household water supply system. Furthermore, the specific energy usage for rainwater supply in the 20 homes was estimated to be 1.52 kWh/kl. This study constitutes important research which provides critical input into strategic urban water planning for sustainable water resource management. The study is focussed on the South East Queensland region of Australia but the methodology developed for the monitoring and assessment of water savings in households with plumbed rainwater tanks will be useful for adoption worldwide by water professionals engaged in alternative water resources planning for urban developments.