How much damage can water do?

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Originally uploaded by modernemama

I feel bad even writing about this, given the amount of flood damage that people in the mid-west are experiencing, but I'm getting increasingly frustrated at the mysterious pool of water that collects under the kitchen sink.
This has been going on for the last three years ,and the last time we said we'd rip out the kitchen sink if it happened again. Well, we're not in a position to do that so I'm sucking it up. Again. (Not literally).
Here's the thing: It's not there all the time, I check for puddles under there regularly; it's not caused by drips from the wastepipe, or from the faucets; we had new lines put in when the dishwasher was replaced last year and they are fine, too. And here's the other thing: The water under the sink is clear. I found this out because we'd put a roll of kitchen towel under there and while it was wet through, it was clean. But it's still water, and that in itself is damaging enough, especially to laminated cabinets.
And of course there is the damage to my psyche. It is driving me nuts. I have to know: Where in the world is that pool of clean water coming from?