You only get condensation on objects that get below the dew point. The dew point is below ambient and the common misconception is that if your parts get below ambient that condensation will form. This is wrong. Depending upon relative humidity the dew point varies. In a high humidity environment the dew point is significantly higher than in a low humidity environment, but unless relative humidity is 100% the dew point is never ambient. In which case it's raining. If you were in the bottom of Death Valley, dew point would be considerably lower than the ambient temperature.
But at any rate, watercooling still uses ambient air through the radiator and as a result coolant temperatures cannot even reach ambient temperatures, so reaching the dew point is entirely out of the question. There is no way you could get condensation with regular watercooling.