Originally Posted by
corporate-wage-slave
When you are next in the United States, go to a REI store. They have plastic bottles that flatten to the thickness of a pancake when empty. I think they're Australian. So no problem with Security anywhere when devoid of liquid - they weigh approx 20 grams, depending on the various sizes available. I then fill these up in BA lounges the world over, no problem at all, frequently to the envy of my fellow passengers when stuck at the end of the tarmac waiting in the queue to get airborne on a hot day.
^I have those too, a couple in my carry on and in my gym bag. And unlike the Tesco bottle suggestion upthread, they are intended for repeat use. "Normal" plastic bottles can degrade and shouldn't be used over an extended period of time.