The b300 figure is to give a sense of scale, its clearly more on the order of milliliters per query than half a liter.

Evaporating water into the atmostsphere is really just recirculating it, it hasn't spoiled the water or destroyed it.

The problem with the 16oz number is that its so clearly wrong that is discredits any other valid arguments. If complaints about ai resource usage want to be taken seriously, forget the water "usage" and worry about the gas/coal/diesel generators pumping carbon directly into the atmosphere. Because that is far more concerning that water getting cycled through the water cycle.