A significant decrease of water disposal to treatment section from a wastewater network (WWN) can be achieved rising internal water reuse through regeneration, i.e. lowering the concentration of one or more contaminants. Zero discharge is the limit case of complete regeneration, although economic considerations may hamper its full application. In this paper the mathematical model of the WWN is extended to consider partial/total stream regeneration. An improved variant of genetic algorithms is used to solve it. Several concepts are formulated, pinpointing which contaminant is better to be removed for decreasing supply water consumption. A case study with six unit operations, four contaminants, one water source and one regeneration unit is analysed. Four regeneration scenarios are investigated, considering (a) the critical contaminant, (b) the contaminants from the bottleneck island, (c) three contaminants-one being outside the bottleneck island and (d) all the contaminants, according to the zero discharge theory. The results obtained are compared against the base case (without regeneration) to highlight the relationship between supply water reduction and internal regeneration. Increased water reuse is related as well to WWN topology optimisation. (C) 2008 Elsevier Ltd. All rights reserved.