So what is "Cannibal Water"? Cannibal Water is water that when diverted, pumped, used, or disposed of after use, destroys the system itself.
Gartrell et al. describe "System Water" as the portion of water going to the ecosystem that is "required to protect the quality of diversions by farms and cities that rely on exports from the Delta or use water locally." (PPIC 2017) What would happen if people started diverting System Water? Salinity would intrude into the Delta, and diversions for agriculture, municipal, and industrial purposes would have to be shut down. The underground parallel is overpumping of an aquifer, allowing salinity intrusion, which then prevents the use of that aquifer.
The water diverted that would result in these negative effects is Cannibal Water, since it consists of water diverters destroying themselves by using water that destroys the system upon which they depend.