Technical and Economic Analysis of Strategies to Reduce Potable Water Consumption in a Library

In Brazil, approximately 93 trillion litres of water are withdrawn annually from surface and groundwater sources, with urban human use being the second-largest water consumer. Therefore, reducing water consumption in buildings is crucial. This study performed a technical and economic analysis of isolated and combined water-saving strategies at the Central Library of the Federal University of Santa Catarina (UFSC). The strategies assessed included water-saving appliances, rainwater harvesting, and greywater and blackwater reuse, individually and in four combined scenarios. User surveys provided data on the frequency and duration of water appliance use and cleaning activities, while on-site water flow measurements enabled the estimation of water end uses. The potential for potable water savings was then determined for each strategy and scenario. The highest savings (77.96%) were achieved by combining water-saving appliances with blackwater reuse, followed by a combination of water-saving appliances, greywater reuse, and rainwater harvesting (65.73%). All strategies were economically viable, except the combination of water-saving appliances with greywater reuse, which showed a negative net present value. The scenario combining water-saving appliances and blackwater reuse generated the most significant financial savings (R$7782.48 per month), with a payback period of 50 months. Given its environmental and economic benefits, these scenarios were recommended for implementation. The study may be replicated worldwide, and one key conclusion is that libraries consume a significant amount of potable water for non-potable purposes, which should be supplemented with alternative sources. It is essential to consider whether the building is already built or under design, as some implementation processes require design modifications.