In order to reduce the effects of water pollution by anthropogenic causes, it is critical to use wastewater treatment plants networks (WWTNs) as an option to remove contaminants that are considered harmful to human health (Bagajewicz and Faria, 2009). These systems are also a milestone for the reuse of water in human activities leading to a sustainable water harnessing. To attain the aforementioned goals, this work intends to develop a systematic methodology for optimal design of WWTNs towards sustainable systems. As a preliminary investigation, a case study has been evaluated using an objective function that prioritizes the environmental aspect of sustainability, being of current investigation the inclusion of the economic and social aspects. The problem was solved formulating an NLP optimization model and the results indicate that the optimal treatment network has a distributed configuration.