Try this to check for a small internal water leak. Let the engine sit overnight until cold. Start the engine and run it for about a mile. Stop the engine and check the inside of the oil filler cap. Do you see condensation? You probably will. If you do touch you finger to it to get a little pinpoint of condensate on your finger. Taste a tiny bit and see if it is sweet. If it is it will also smell like anti-freeze. Now replace the cap and run the engine for 10-15 miles or so. Does the condensate evaporate completely. If so, then you probably do have a small leak, HOWEVER, as long as your engine is getting up to operating temperature daily in order to cook off the small amount of coolant you will probably be okay for a while anyway, until you can find the internal leak. If you just make short trips and not getting your engine hot enough, long enough to cook off the water then you are working on a major problem. Your oil looks pretty clean, so my bet is you probably have started a minor seepage inside. Let us know what you find out. Oh, one other thing... take a look inside your coolant overflow tank. See any signs of oil residue in there?
2001 SSEi- black; stock 92K
1995 Vette; Competition Yellow; stock; 38K