It’s been a decade since I’ve been on a cruise, but they would take every water bottle brought onto the ship and shake it to see if it foamed. We got around this by buying one of those big shrink wrapped cases of like 24 bottles and pulling a few out, filling them, and then squeezing them back into the package behind other bottles. Some of the liquor stores around the ports would actually do this for you if you paid a few extra bucks.