Water in the oil is a natural consequence of the condensation of atmospheric humidity. Whenever the engine is started , warmed and then shut down this process occurs. This is why short trips are so hard on an engine and will necessitate more frequent oil changes. If the car is driven longer distances regularly some or most of the H
2O will evaporate off, depends on the oil temps, ambient temps, dewpoint, duration and load during the trip.
This is the main reason that the oil should be changed immediately prior to long term storage(most of us northerners are all too familiar w/ this activity
) and not driven until spring. It is also why I disagree w/ the folks that say to take the car out occasionally during our all too long winters for a little exercise. The exercise is good for the seals and bearings but the condensation (IMHO) negates the benefits, plus you get corrosive substances all over your immaculate wheels.