I'm just waiting for someone to invent titanium water...then we can do some proper weight saving.
.
Had you considered trying a bottle of de-hydrated water (simply add water and you get WATER !!)
Alternatively carry a small cylinder of Hydrogen and a larger one of oxygen - mix the contents in a ratio of 2:1 (2x Oxygen and 1 x Hydrogen) Shake well and the result is water.