Actually, no, it isn't. Leukotape on the other hand will stick to a Camelbak nicely.

Duct tape doesn't stick nearly as well to things as people like to pretend it does. It doesn't stick to my skin, doesn't stick to silnylon (then again, nothing does), and doesn't do much for a bladder under any kind of pressure. As I found out the hard way.

For the SAR outings I am asked to bring a Nalgene, hard sided, in case the bladder fails.