We may be contributing to it, but so is every other life-form, if its going to happen its going to happen; it'll all sort itself out in the end, like it did before.
In 30,000 years this'll all be forgotten about, why worry. What life-forms remain on earth at that time, will be perfectly happy, will have adapted to whatever resources there are and life (maybe not us though) will merrily continue on its way.
We ALWAYS assume its wrong/bad because of how it affects US (isnt that arrogant in the grand scheme of things, like we are the most important?) which is what this thread is all about in fact, how our water usage affects US. The water will ALWAYS end up back where it came from, in the atmosphere or in the oceans. It always does. Why are we worried about it, because theres too many of us with inadequate storage facilities.