Water reuse can be a highly sustainable means of producing water resources. In regions where fresh water resources are limited it is much more energy-efficient to remove the relatively efficiently separable impurities from used water, than it is to remove salt from saline or brackish water.
Even in areas where fresh water is abundantly available, water reuse can have additional benefits, for example plants can benefit from the nutrients found in municipal wastewater, hence reducing requirements for chemical fertiliser addition.
There are, of course, social and technical challenges around some forms of water reuse (particularly direct toilet to tap). However we predict that acceptance & adoption of sustainable water reuse practices will continue to increase with time.