[marsokod]

Water is the space fuel of the future. Well, at least the space oil of the future - if you start mining asteroid and comets, water is one of the best component you can get: good for any life around, quite a good solvent if you need one, and more importantly can be a fuel like this or be transformed into oxygen and hydrogen, which is rocket fuel as well.

Also, good luck depleting the water on Earth with space travel. There would be other issues way before this happens.

[politician]

Right, like figuring out why you would want to bother lifting significant amounts of water mass into space in the first place.