First, check your coolant level and make sure it hasn't dropped. If you only start it once in a while and/or don't drive very far, that will happen. The machine needs to get up to full operating temp for a few minutes to burn out the condensation that naturally occurs inside the engine. If the amount of water appears to be very slight and is mainly on the cap and not mixed in with the oil, try letting it idle for about 30 minutes. I'm hesitant to recommend running it hard (which would eliminate it quicker), just in case there is actually a major problem where coolant is mixing with the oil.
You'll find in some weather conditions the condensation is more prevalent, I notice it more with a rapid temperature change in a short time. If the oil on the end of the dipstick is milky this would be of concern, might try loosening the drain plug after it has sat for some time to see if an water/antifreeze comes out, it will leak before the plug is completely out.
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