What about the water cycle? "Using" water doesn't mean "using it up" – if you water a field from a well, some portion of that water goes back into the ground from whence it came, largely unmolested. For that matter, when I flush my toilet the water isn't destroyed, it just goes to be cleaned up and released back into the wild. I'm still not sure if the cleaning process is a challenge because of the quantity of the liquid or the quantity of the contaminant (with low-flow toilets not changing the contamination of the water at all).

What are the real bottlenecks in our water system?