Water and other liquids seem totally harmless and it doesn't seem to make a whole lot of sense that you can't bring bottles of water or cans of soda, even the unopened ones, through airport security. \
However, there are chemical explosives in the world and chemical formulas that can create explosions. These chemicals can look as harmless as water. \
Even someone with a small amount of scientific knowledge can learn how to obtain these chemicals and perform dangerous actions with them. And even though you may have no such intention in your head when you walk through security with your water bottle, the person behind you may have darker thoughts in their head and for the safety of everyone, no one can be allowed on a plane with liquids when this is a possibility. \
It is better to have a safe flight and perhaps be a little bit thirsty. \