I was also worried about it, so I tested it first empty and slowly pump it until it reached about 90psi! I held it there for about 5 mins and when nothing happened then I know I was good! One thing though, as the pressure goes up, air will start to come out at he cap, so you have to tighten as you go! I also wrap a few rounds of white water pipe tape (the one you use to join two water pipes at home) on the threaded mouth of the water bottle and that help seal it, but you still have to tighten as the pressure increase!
BTW: after the test, it would be very, very tight (and I think only Lani can open it at this point! ), so you have to pump the pressure up again until you feel the air coming out, then you very slowly start to untighten the top cover, when it's loose enough, then you turn off the pump!
XELOR!!!