In this paper, a new flexible wastewater treatment scheme is proposed to be used within the framework of wastewater reuse (REUSE). From a configuration where the water is treated to guarantee normative constraints, we propose a flexible configuration able to adapt, in minimal time, the quality and the quantity of water to usage. In other terms, the proposed scheme is able to treat water for purpose. Using model analysis and simulations, we show how a simulation platform may be used to demonstrate the flexible characteristics of the scheme, in particular when dealing with the decoupling of water fluxes and the different forms of nitrogen contents in the output treated water.