Supposedly this pack can hold a pair of water bladders.  They sell their own re-branded Source bladders as a related item to this pack (both 2 and 3 liter models).

http://www.eberlestock.com/miva/merchant.mvc?Screen=PROD&Store_Code=E1&Product_Code=X3&Category_Code=TP

Either I'm screwing something up, or there's NO WAY IN HELL you're cramming a 3 liter bladder in either of the sleeves designated for this purpose (let alone two of them...)  The fit is just WAY too tight.  

I've tried a 3 liter new-style camelbak (which is a wider design than the classic ones), my 3 liter source which is the same thing Eberlestock is selling, and a classic design camelbak, all with zero luck.  Fully filled, 3/4 filled, etc. makes no difference.

what the flying hell?

I removed the stitching that separates the two halves. Fits a 3 liter and then some quite easily.