[astrodust]

When it ends up in the environment and eventually the ocean, fresh water is destroyed. Period. It is no longer fresh water. You can reconstitute it at great expense, manufacture it practically.

When it's pulled from deep, ancient reservoirs that get replenished very slowly it's slowly destroying the reservoir. Given the time-scales involved, where tens of thousands of years or more are required to re-fill these, it's effectively permanent destruction.

Your argument is extremely misleading. It's like saying gasoline isn't destroyed by cars because you can always reverse the process.