Water pollution and scarcity of water is a life-and-death problem the human being is facing.It is worthy of investigation of evolving water-using processes to reduce both fresh water consumption and wastewater production.This paper approaches the optimized design of water-using processes

i.e. wastewater minimization.The concepts of process source and process sequence are introduced.For reuse process of a single contaminant and multiple contaminants along with regeneration and reuse process of a single contaminant

a new computation method is addressed respectively

which is named as step by step linear programming method.From the beginning

the processes are sectionalized or collated according to the limiting operating data of lean streams

and then the matching between rich streams and lean streams(water sources) is optimized step by step in accordance with the collated processes

ultimately the design of water-using network is attained.Four examples are solved to demonstrate the effectiveness and convenience of the new method.