## 4 Discussion  
As observed by [20], the supply of CMPs through the conventional potable water distribution network (Alternative A) is quite unfeasible, given the high potable water tariff practiced by CEDAE [2], especially for larger industrial demands. In this case, the cost of water from the conventional network was at least 40% higher than the cost of water supplied by water tank trucks. Among all four water supply alternatives analyzed for the listed CMPs, it was found that those based on the use of reclaimed water are the most feasible by a large margin. With a present cost of BRL 5.27 per m\({}^{3}\), representing, therefore, 18% of the tariff charged by the water company for water supplied through the conventional distribution network system and 21% relating to the cost of water transported by water tank truck, Alternative (D), using reclaimed water supplied through pipeline network, was the most attractive alternative for potential consumers. Alternative D presented an IRR of 164.8% and an IL of 13.87, which can be considered as an investment of excellent return, with a short payback period of approximately 3 months. In a way, these results contradict [26] who stated that wastewater reuse projects are not viable only in the short term. However, these authors referred to wastewater reuse for agricultural purposes, in areas where the \"willingness to pay\" is usually low [43] and budgets for water payments are negligible or non-existent, which leads to longer payback periods. As already mentioned, and supported by [1; 21; 29], the reuse of effluents from WTPs for urban and industrial water demands and applications presents the greatest feasibility in urban areas such as the Caju neighborhood and in most of the MRJ as well. In addition to the perspective of reduced production costs for industries such as CMPs due to the use of a cheaper industrial water, other aspects favored the alternative using reclaimed water, either by pipeline or by water tank trucks: (1) the availability of a secondary effluent of excellent quality at the Alegria WRP/WTP, indicated for some industrial purposes [18; 44; 45], if particularly evaluated according to the requirements of Brazilian concrete production requirements and standards [6]; (2) The Alegria WRP/WTP has a steady and fair performance history in the water supply of Porto Maravilha works in the last decade [11; 12; 25], indicating both quantity and quality security for the supply of reclaimed water to the CMPs; (3) a considerable part of the costs involved in the production of reclaimed water are already incorporated into the daily operation of the Alegria WTP, which aims to meet the high environmental restrictions and water quality requirements for effluent discharge into the local water body (Canal do Cunha) [10; 11]; and (4) the reduced distances (less than 2 km) between the Alegria WRP/WTP and the cluster of potential industrial water consumers examined (the CMPs) [2; 46]. The estimated production availability of reclaimed water at the Alegria WRP/WTP--2.5 times higher than the estimated water demands of the CMP cluster--demonstrates the great potential for reclaimed water supply due to the presence of several other companies and industries in the studied region/neighborhood [25]. Thus, the reclaimed water supply can be expanded, with a few investments in the existing facilities (WRP), therefore increasing its attractiveness due to the economy of scale factor [10]. Comparing, more specifically, the two supply options which use reclaimed water (transported by water tank trucks or pipeline), it can be highlighted that the pipeline alternative provides more security and reliability due to the greater automation of its operational requirements, in addition to a more optimized logistics of the reclaimed water supply [13]. The alternative using a reclaimed water pipeline could become even more feasible and economically attractive if the existing and non-operational concrete tanks of the Alegria WTP could be used as reclaimed water reservoirs.