It is generally known that the ecological services provided by aquatic ecosystems and the water industry are facing increasingly complex challenges: the demand for water is continuously rising, causing the rapid exhaustion of existing water resources. Urban population growth and changing lifestyles, implying more intensive water use
[1] and increasing water pollution
[2], are the leading causes of this phenomenon. Besides, future climate changes will involve higher temperatures and changes in the intensity and patterns of precipitation, leading to more frequent droughts, as well as reducing water quantity and quality, in southern Europe and the Iberian Peninsula
[3][4]. Thus, the urban water cycle is affected by climate change, but it is also contributing to climate change. Indeed, water potabilization processes, the delivery of water to consumers, and the treatment of wastewater use significant amounts of energy, contributing to increasing CO
2 and other greenhouse gas emissions
[1][5][6]. Therefore, in the face of this scenario, it is important to implement water sustainability, promoting water use efficiency by reducing water consumption through the adoption of efficient products or devices (e.g., taps and showers), reducing waste and losses, and by reusing and recycling water
[7]. Public indoor swimming-pool facilities use large amounts of water and, consequently, energy, because of their particular characteristics: (1) the relatively high temperature and humidity levels in the pool room; (2) the evaporation caused by pool usage; (3) the use of warm water for pools and showers; and (4) the requirement of a water treatment system
[8][9]. Furthermore, users’ number and behavior, the variety of services provided, the operating patterns
[8][9], and the quality of indoor water and air
[10][11] also influence the aforementioned characteristics. Nevertheless, to our best knowledge, research concerning the impact of these facilities on urban water demand is scarce. Some research has focused on residential swimming pools, revealing that pools have a very high impact on urban water demand and consequently on ecological integrity and the services provided by freshwater ecosystems
[12][13][14][15]. However, approaches concerning municipal and public indoor swimming pools are even scarcer and, in some cases, very preliminary
[16][17][18][19]. Similarly, research concerning the recycling and reuse feasibility of pool filter backwashing is also very scarce
[20][21][22][23][24]. Therefore, to contribute to filling this information gap, the aim of this research is: (a) to determinate the water demand of a municipal indoor swimming pool complex; (b) to propose water use efficiency measures, analyzing their feasibility and costs; (c) to evaluate the possibility of recycling and reusing the water from swimming-pool filter backwashing.
Municipalities may use the results of this study to implement and improve measures to achieve greater water use efficiency in their infrastructure.