I bought a bottle of Nestl's filtered water (100 oz bottle) and filled the hydration pack. There was still 12 ozs left in bottle.  I can see an oz or two difference due to manufacturing issues (1% or 2% is acceptable) but with a capacity of 12% less than stated I think this should be pulled from shelves and remade.
The pack it self is a nice pack. Pockets are a bit small but it is only an 18-Litre pack.  Would be nice to have the side pockets for water bottles be large enough to handle a liter bottle (my bottle of choice) Also need a belt extender for bigger hikers.