If the room is a VERY warm room (for whatever reason), the air in the room will HOLD an awful lot of moisture. When that moisture in the air comes in contact with a COOLER surface (and it's a relative cooler that I mean; not necessarily COLDer surface), the moisture will condense out of the air and form on the cooler surface. The more moisture there is in the air, the more condensation you will have.
Now, your room may be warm for a number of reasons: 1) Outside wall that gets a LOT of sun/heat (possibly poorly insulated), 2) the room sits above a warm room, like a kitchen, laundry room, or a room w/a how water heater in it, 3) it has a higher ceiling or it's in a corner of a house where there isn't much circulation, or where warm air tends to 'collect', or 4) I think you get the picture.
In short, if you can reduce the heat, you effectively reduce the moisture content. And as Dave-o said, check the water temp itself. The next time you flush, see how warm or cold the water is. The colder the water, the more likely you'll get condensation.