What causes the toilet seat lid to be covered with condensation?

This is similar to the problem of condensation appearing on the outside of a water glass. Water vapor condenses on a surface that is cooler than the temperature of the water vapor.

I had been wondering the same thing about my own toilet seat (it affects the seat in my case, and not just the lid, which was quite disconcerting the first time I noticed it!). The explanation I have puzzled out is this:

* The water in the toilet bowl has had all day to warm up. Considering the density of water, it will take it quite a while to cool back down.

* However, the toilet seat and lid are relatively thin pieces of plastic, so they cool down more quickly than the water.

* I'm guessing there is somewhat more water vapor in the toilet bowl than anywhere else in the house, and considering it is trapped by the (now cool) closed seat lid, the water vapor decides that the toilet seat lid looks like a great place to settle down for a while.

If you wish to avoid this, I'm going to hazard a guess that leaving the seat lid open would do wonders, since the vapor would then have a much easier time leaving the vicinity and many more places to settle.

I usually turn my a/c down (to a lower temp) when I get home at night, which I initially thought was causing the above. I think it's just as likely, though, that the natural cooling that occurs with the onset of evening would cause the same result.