condensation forms when object is colder then the air around it, and the relative humidity is high. For example:
in a 75°F room, if your waterblock is 70°F with relative humidity is 80% you will start to get condensation.
in a 55°F room, with relative humidity of 20%, my block temp can be... well that is not on the chart because 40% humidity allows the block to be 32°F (freezing point)