They do chop up a glacier once in a while, I guess, but it's pretty much just going back and forth.
Wayne Hanson wrote about this in Govt Technology mag recently. He points out that the water in your morning coffee might have been excreted by a Neanderthal or have been part of the iceberg that sunk the Titanic.
Since the Industrial Rev, we have added 6 billion people, all vying for potable water and adding things to it such as drugs and poison.
Birth control substances may be contributing to prostate cancer.
Traditional water treatment does not eliminate these pollutants. One authority recommends waterworks be changed to three pipes--drinking water, nonpotable water for irrigation, and sewerage.
Desalination is still pretty expensive, but they are working on it. Techniques for transforming sewerage into drinking water are pretty far long--and not just in space stations.