I’m sorry to say that even the relatively-expensive, relatively-heavy military bags I bought don’t score very highly on this point.<br><br>I’ve tried rolling the tops and strapping them as tightly as I can, and they’re fine- until laid down flat, or put under pressure. When that happens, water works it’s way through the rolled-up spout and drips. Slowly, but it drips.<br><br>They do have the belt loops, and as long as they’re carried upright, with no pressure on them, they seem fine. Still, that’s one more point that the Platypus bottles have in their favor- at least the one I’ve used has never leaked- and the Platypus bottles stand upright when full. The military bags do not, making it much harder to avoid it's leaking.<br> <br>So far, the only advantages the military survival bags have is flatness and the belt loop- and easier drying, because of the larger mouth. <br>