Unless the rockets are going to use hydrogen from the water as fuel then no, it's pointless. Hydrogen is a very unstable form of fuel, which is the reason they don't allow cars to run on them. It wouldn't be economically viable to risk an expensive mission using this fuel, unless they were sending out say a hundred duplicate probes and allowing a number of them to fail. Even then it would be even more risky entering an atmosphere holding this as fuel. Feel free to vote me down and call me names though..