The definition of the water/wastewater allocation problem is discussed as it was originally defined by Takama et al.(1) how this concept was modified, and sometimes simplified, through time, as well as additional issues that is believed are still not properly addressed. A few attempts are reviewed where parts are pointed out, and the addition of water pretreatment units are discussed, and further investigation in to the impact that proper modeling has on predictions of freshwater consumption, total annual cost and zero discharge cycles. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 668-689, 2010