Probably the most efficient way would be something you could burn to yield water, like a hydrocarbon or carbohydrate, if you had to liberate the water by chemic

Probably the most efficient way would be something you could burn to yield water, like a hydrocarbon or carbohydrate, if you had to liberate the water by chemical process. Or you could use something to contain the water in a solid structure, like a sponge or plant tissue. None of these options makes a lick of sense to simply accomplish transportation of water.