Well, condensation occurs when the temperature of something is below the dew point and the dew point depends on the relative humidity. Now, when the ambient temperature reaches the dew point the water vapor in the air condenses out and you get rain, dew, or condensation. So, if it isn't raining in your room already or the walls aren't dripping with condensation then we can safely assume that the ambient temperaure is above the dew point. Anyway, if your water temperature doesn't go below ambient then you shouldn't have to worry about condensation. Also, if your only using straight water cooling (no peltiers) and your only using a heat exchanger cooled by ambient air, like a radiator, your water temperature shouldn't go below ambient. After all the radiator works by transfering the heat from the water to it's metals walls and on through to the outside air. Remember heat transfer only occurs from warmer objects to cooler objects. So, in order for the water to transfer heat to the radiator and eventually the air the air must be cooler than the water and once the water temperature starts to approach the ambient air temperature the heat transfer slows down and stops. So, with just a radiator which is cooled by air at ambient temperature your water temperature shoould never go below ambient and condensation shouldn't be a problem.