A common source of leaks in O'DAYs (and some other brands too) is the cockpit scupper (drain) at the aft end of the cockpit, there is a rhru-hull fitting in the little well at the aft end of the cockpit that connects by a short hose to another thru-hull located just above the waterline on the transom. Those thru-hulls were plastic and could develop cracks or the hose can rot out. That can create a freshwater leak every time it rains, or a "raw" water (what the boat is floating in) if that drain ends up below the waterline due to people in the cockpit. A bit of a squeeze to access that drain to check/repair, nimble folks may be able to crawl into the cockpit locker to reach, others have installed an 8" inspection port in the aft bulkhead of the cockpit.
If this boat has been sitting outside for a while, it could be condensation or just a lot of very little leaks when it rains. The "good" news is that since it is collecting, there do not seem to be any leaks below the waterline! Otherwise it would have seeped out.
Here is one advantage of sailing on saltwater like I do! Taste the water and you know if it is rain or a hull leak. I had a leak in the hull-deck joint of my DSII once, a little sealant there fixed it. BTW, I grew up sailing on a CAL 21. GREAT boat, but not really setup for daysailing off a trailer. We had ours on a mooring all Summer and stored on a cradle for Winter as a boatyard. The Keel design worked great for us (with a few wrinkles), but that was the boats best and worst feature at the same time! At least cockpit drains were not complicated, water could just drain around edges of the cover for the keel well, and through drain holes in that cover.