This paper addresses the design of distributed effluent treatment systems. In the case of single contaminants, targets are first set for the minimum flowrates in a distributed effluent treatment system. Design methods then allow the targets to be achieved in practice. Previously published methods failed to address important features of the design for multiple treatment processes. In the case of multiple contaminants the treatment network is developed in a staged approach by repeated use of targets and design. Minimum flowrate is not guaranteed for multiple contaminants, but the designer is guided ton ards the best solutions. Overall, the paper presents improved methods for the design of distributed effluent treatment systems and extends the concepts to retrofit cases.