The urgency of water crisis has attracted more and more research in the field of process systems engineering. Starting from describing the status of water crisis globally and in China

this paper introduces water crisis related policies from government and opinions from academic circles. Documentation retrieval for water network and virtual water studies since 1994 is conducted. The topic is systematically reviewed in three levels according to the scale size. ① Water network integration and optimization in a single enterprise

including water using network (WUN)

wastewater treatment network (WWTN)

total water network (TWN)

complete water network (CWN)

and three special problems

which are cooling water systems

WUN with internal water mains

water network for batch processes. Water allocation and heat exchange network (WAHEN) problems and simultaneous process synthesis with heat and water integrations are also included. ② Inter-plant multiple water network integration

including water networks integration in eco-industrial parks. ③ Virtual water and water footprints studies across prefectures/countries. These studies are very useful in water conservation

wastewater reduction

energy efficiency improvement in enterprises and eco-industrial parks

and also provide the basis for policy arrangements for governments particularly those of water scarce areas.