My Basement Has A Mystery Leak

This morning at 4:45 AM I went down to my basement to grab some clean underwear from the dryer.  As I turned down the stairs, it smelled like wet stone.  It's that musty smell you sometimes experience after it rains.  I soon found the source.  I had about 4 gallons of water on the floor of the basement.  The joys of being a homeowner!Immediately I thought it might be our furnace that is from the civil war period.  After checking the furnace, I soon realized that's not the problem.  The water was basically from around the water heater and spilling towards the right under the workbench.  (which you can see in the picture).  It did rain last night, so I thought maybe it was leaking in from the ground.  Not having much time, I threw down a few towels and ran off to work and hoped that it wouldn't get worse.

When I got home I checked the ground outside where the leak could have been coming in.  It was totally dry.  So far the leak hasn't returned.  I sucked it all up with a shop vac and no more water.  I've ran the water heater and inspected it for leaks.   Nothing.  The boiler furnace isn't leaking.  I know some times that a water heater can have a small leak and then get plugged back up with sediment in the tank, but I'm not sure if that is what's going on.  I certainly don't want to spend several hundred dollars fixing something that may not need to be fixed.  Have any ideas?  Because I don't.  It's a phantom leak.