## 1 Introduction  
The Guandu Water System supplies 70% of the Metropolitan Region of Rio de Janeiro (MRR)) potable water demands and is structured mainly from a diversion of 120 m\({}^{3}\)/s from the Paraiba do Sul River basin to the Guandu River basin, of which 45 m\({}^{3}\)/s are captured for treatment and distribution [1]. This complex system involves high costs due to the stages of diversion, treatment, pumping, and distribution, and this complexity is reflected in the tariff paid by the consumer, one of the highest in Brazil [2]. Recently, this system has been facing several difficulties, aggravated by the pollution of its main water sources, as demonstrated by the severe water shortage crisis that occurred in 2019/2020, generating supply problems for much of the Rio de Janeiro population [3, 4]. In this context, the search for alternative and more sustainable and economically advantageous sources of water has become a high priority. Among the available options, the reuse of effluents from wastewater treatment plants (WTP) is configured as a strategic tool for water resource management and supply [5, 6]. Wastewater reuse can reduce industrial production costs and benefit the environment by providing a more rational use of water resources, as well as reducing the discharge of pollutants into water bodies [7, 8]. In addition to optimizing the rational use of water, reuse provides an increase in the water security of the watershed [9, 10]. Several authors identify urban and industrial water demands fulfilled with reclaimed water from larger WTPs as the typology that presents greater technical and economic feasibility, especially in more urbanized areas [2; 5; 11; 12]. Some of the most impactful aspects pointed out in these studies were: distance between potential producers and consumers; flow rate of reclaimed water demanded by the consumers; requirement/guarantee of minimum flow rate and quality of reclaimed water production; and potable water tariffs from the conventional water supply system. However, the reuse of wastewater from WTPs in MRRJ is still incipient and basically supplies the internal demands of the sanitation companies that operate them, such as equipment cleaning and clearance of sewer pipes. There are isolated initiatives as well aimed at specific demands in which reclaimed water transported by water tank trucks from Penha WTP are used by COMLURB to wash and clean streets and public fairs [1; 13; 14]. There are many examples of market niches and companies whose water demands can be partially or fully met with reclaimed water, generating new sources of revenue for the sanitation companies as well [15]. In Brazil, however, there are only a few successful \"cases\", such as the AQUAPOLO system, which uses almost 1 m\({}^{3}\)/s of reclaimed water from the ABC WTP and its wastewater reclamation plant (WRP) pumped through a 17 km long 900 mm diameter pipeline to supply the water demands of a cluster of 13 industries in Sao Paulo [16]. According to [17], the reclaimed water from distinct WRP/WTPs in the MRRJ has high-quality characteristics which fulfill the standards and requirements for its use even in more restricted purposes such as the water supply for cooling towers. Several authors indicate that the concrete production industry can use the reuse water produced by a WWTP as a raw material, in some cases even increasing concrete performance parameters [18; 19; 20]. According to [21; 22; 23], the use of treated sewage does not cause deleterious effects on concrete, and the criteria used to determine the water quality for concrete production are entirely different from the parameters required for potable purposes [24]. Although reuse is a practice already known, institutionalized, and widely used in several countries, in Brazil it still faces several challenges, including lack of regulation, and technical and practical knowledge about the subject as well [25].