Alternative water supply systems to achieve the net zero water use goal in high-density mixed-use buildings.

• Building typology affected the performance of alternative water supply systems. • Alternative water supply scenarios were analyzed against sustainability criteria. • Alternative supply options in the local context were evaluated. • Net zero water use was not fully achieved through alternative supply systems. • High potable demand was a deterrent against achieving net zero water use target. The water crisis in urban areas has manifested concerns for sustainable water supply practices in buildings. Although efforts have been taken to reduce freshwater consumption through demand management techniques and alternative supply strategies to some extent, when it comes to a more sophisticated concept like net zero water (NZW) use, practically implemented cases are rare. Due to building characteristics, geographical location, and uncertainties in the decision-making process, the feasibility of the NZW target needs to be explored. This research used a framework with a case study in Melbourne, Australia, to evaluate alternative water supply scenarios that may have the potential to approach this target in mixed-use buildings. Alongside their technical performance in reducing mains water consumption, wastewater discharge, and stormwater runoff, alternative systems were analyzed against environmental, economic and social aspects of sustainability. For each sustainability criterion, an indicator was selected. Through the proposed scenarios, the goal of NZW use was not fully achieved. However, the three performance indicators exhibited considerable reductions in net water flows. Supposing that the three sustainability aspects are equally valued, a hybrid utilization of rainwater and treated greywater may be the preferred option for mixed-use buildings in a temperate climate. [ABSTRACT FROM AUTHOR]