I don’t understand why filtered waste water excluding solid waste ie:bath and shower water in high rises is not used to flush toilets on the floors below and/or ran through a turbine to create electricity. There would be 2 drain systems. Drain 1 for ejected waste water that would not be reused. Drain 2 water would be filtered and treated into a tank below each floor which could overflow into more tanks in even lower floors . This water would be used to flush the toilets. The filters could be back flushed into drain 2 periodically to remove any waste.