Mysterious bilge water

I put my new to me J24 in the water on Wednesday. It's Friday afternoon. The bilge was about half full. It did rain pretty hard, so at first I wasn't to concerned. But then I tasted the water and it was brackish. So I suspected there was a leak from below mixed with some rain water.

There is a drain hole in the back of the bilge on the starboard side. That's the source of the very slow leak. Where does that drain hole come from?

Pics attached